For an Animal to Move in One Direction,its Muscles Must

Question

For an animal to move in one direction,its muscles must do all of the following except  
A) exert a force in the opposite direction.
B) overcome the effects of friction.
C) exert a force in the same direction.
D) overcome the effects of gravity.
E) spend energy.

Accepted Answer

For an animal to move in one direction, its muscles must exert a force in the opposite direction to the intended movement (action-reaction principle), overcome friction and gravity, and spend energy. Exerting a force in the same direction as the movement would not contribute to the movement in the intended direction, making it the exception.