 A close up of two young bull elk Cervus elaphus, in an aggressive battle
 Woman climbing cliff, Boulder CO
 Green tree frog sleep on the stone. Frog sleeping in an aquarium at the zoo, the frog humbly sleeping
 Netherlands, Blaricum, Heathland or moorland called Tafelbergheide. Charolais cattle. Young bulls challenging each other
 Young man in Santiago Chile engaged in parkour by balancing on a handrail high above the ground with blue sky and tall white building in background
 Paramedics dressing mannequins in preparation for use in a GMICE major incident exercise in Newquay Harbour in Cornwall.
 Hippo, (Hippopotamus amphibious) challenging in Kwai river, Botswana
 Close-up of trail running shoe on challenging rocky terrain. Male runner's legs working out on extreme terrain outdoors.
 Skillful young business woman balancing between reward and risk in challenging corporate environment
 Portrait of two beautiful young female rivals sitting side by side on bench and looking at each other with challenging
 An aerial view of West Maui off Ukumehame Beach Park, Hawaii, USA.
 Laguna Torre with view of Cerro Torre, El Chalten, Patagonia, Argentina, South America
 Students and teacher walking in forest
 Laurie Brownell (R) at Needles Overlook, Canyonlands National Park, UT USA
 A climber's stacked fists in a crack.
 father and son challenging each other in a chess game
 Young African American Woman with Challenging Stare
 Teachers helping students walk on stilts
 climbers the help,support and interest
 Hartebeest antelopes with horns in the fighting pose at a safari sunrise. Photographed at the ADDO Elephant Park in South Africa.
 A Kelp Crab warns the photographer to keep his distance, Oregon, USA (Pugettia producta)
 Cute child playing with building blocks and developing fine motor skills and problem solving, Townsville QLD, Australia
 Netherlands, Blaricum, Heathland or moorland called Tafelbergheide. Charolais cattle. Young bulls challenging each other
 pug challenging
 Volunteers of the Newquay RNLI crew participating in a GMICE (Good Medicine in Challenging Environments) major incident exercise in Newquay.
 Businessman climbing the corporate ladder of success
 Close up of an athlete's feet wearing sports shoes on a challenging dirt track. Trail running workout on rocky terrain outdoors.
 A close up of two young bull elk Cervus elaphus, in a battle during the rut in Jasper National Park in Alberta, Canada.
 Hiker revels in the view after a challenging, yet rewarding hike to the top of the Enderby Cliffs, overlooking Enderby, in the
 Kayaking on the Tryweryn River, Wales.
 Cerro Torre, El Chalten, Patagonia, Argentina, South America
 businesswoman in challenging pose between columns looking at you.
 A boy outdoors in a woolly hat wearing shorts and wellington boots, striking a pose with an outstretched arm.
 A climber's stacked fists in a crack.
 Portrait of botanist sitting in laboratory
 Young provoking teenage girl, portrait on white background
 Young girl at a treetop adventure park in Germany.
 power, balance and motivation
 Sightseeing in Georgia can be challenging for the driver, road signs warning for 9 % steep decline near the Gelati monastery
 Teachers helping students walk on stilts outdoors
 Studying for challenging Math Test
 Netherlands, Blaricum, Heathland or moorland called Tafelbergheide. Charolais cattle. Young bulls challenging each other
 Adventural tour on challenging trail in forest
 The Newquay Inshore rescue craft and its volunteer crew participating in a GMICE (Good Medicine in Challenging Environments) major incident exercise i
 happy and joyful mountaineers
 Closeup of male feet run through rocky terrain. Cross country running with focus on runner's legs.
 Two bull elk , Cervus elaphus, fighting in a meadow
 Hiker revels in the view after a challenging, yet rewarding hike to the top of the Enderby Cliffs, overlooking Enderby, in the
 successful mountaineers on the summit rocks
 Sign post for a challenging bike ride in the Lake District, England, UK.
 businesswoman in challenging pose between columns looking at you.
 A boy outdoors in a woolly hat wearing shorts and wellington boots, striking a pose with an outstretched arm.
 successful & determined & self-confidence
 Portrait of botanist sitting in laboratory
 Building blocks forming a challenging puzzle isolated on a black background
 Two climbers challenging Aiguille du Midi in French Alps, Haute-Savoie, France
 Challenging and dangerous mountaineering positions
 The Most Challenging Links in the World Slogan at the Practise Putting Green at Carnoustie Links in Angus Scotland.
 Muslim girl goes against the flow and walks alone challenging the waters of the Zayandeh river by the Si o seh pol bridge - Isfahan, Iran
 Studying for challenging Math Test
 Netherlands, Blaricum, Heathland or moorland called Tafelbergheide. Charolais cattle. Young bulls challenging each other
 Hiking on an exciting and challenging trail in forest
 Mannequins waiting to be used in a GMICE (Good Medicine in Challenging Environments) major incident exercise in Newquay Harbour in Cornwall.
 A six year old boy walks across a foot bridge by himself.
 Cross country running. Closeup of male feet run through rocky terrain. Focus on shoes.
 A close up of two young bull elk Cervus elaphus, pushing and shoving during the rut in Jasper National Park in Alberta, Canada.
 Hiker revels in the view after a challenging, yet rewarding hike to the top of the Enderby Cliffs, overlooking Enderby, in the
 Mannequins waiting to be used in a GMICE Good Medicine in Challenging Environments major incident exercise in Newquay Harbour in Cornwall.
 Young man with eyes closed pushing hands forward walking in darkness with help of intuition.
 portrait of blonde caucasian child three years old with blue shirt, at breakfast, looking with challenging funny face, with food on dish, sitting in
 cliff the climber silhouette
 Portrait thai boxers showing their muscles
 Botanist looking through microscope
 Man With Artificial Leg Posing For Selfie With Female Partner Whilst On Summer Beach Vacation In South Africa
 Man jumping in dust cloud during freerunning exercise
 challenging struggle and success summit
 Thailand, Koh Phangan, Sportive woman doing yoga on the beach
 Woman standing on paddleboard in lake
 Studying for challenging Math Test
 Austria, Tyrol, snowshoe hikers running through snow, man falling
 Hiking on an exciting and challenging trail in forest
 A Rescue and Firefighting Aircraft Simulator floating on the sea and being used in a GMICE (Good Medicine in Challenging Environments) major incident
 Tattooed man doing parkour
 Man practicing yoga in studio
 Two bull elk Cervus elaphus; pushing and shoving each other
 rugby players challenging for ball in short line out
 Volunteers of the Newquay RNLI crew participating in a GMICE Good Medicine in Challenging Environments major incident exercise in Newquay in Cornwall.
 Challenging hole on luxury golf course with water and sand
 portrait of blonde caucasian child three years old with blue shirt, at breakfast, looking with challenging funny face, with food on dish, sitting in
 Close up of woman holding her foot in a yoga pose, fingers and toes, with face in the background.
 Portrait thai boxers showing their muscles
 Technician analyzing water samples
 Man With Artificial Leg Posing For Selfie With Female Partner Whilst On Summer Beach Vacation In South Africa
 Female rock climber looking up at challenging route on cliff and smiling
 challenging rock climbing and success
 Man climbing Peapod a severe challenging climb on Curbar Edge Peak District Derbyshire England UK roped to steep rocks
 Looking at the final section of exposed, knife-edge trail near the end of the Angel's Landing hike in Zion National Park in Utah
 Studying for challenging Math Test
 A climber poses on the summit of Aiguille de la Belvedere in the Chamonix Alps, France
 Hiking on an exciting and challenging trail in forest
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