Answer
b. a snake
Work Step by Step
During a salmon run, salmon must swim back to the waters where they were born, battling against gravity to leap up waterfalls and rapids to return to their birthplaces to spawn.
A sparrow goes against gravity each time it lifts itself up into the air to fly. Gravity also affects the sparrow's flight, and the bird must continuously fight against this force to keep itself airborne.
Grasshoppers' legs must battle gravity for them to be able to hop around.
Only snakes, which normally travel horizontally rather than vertically, will be least affected by the force of gravity.
