Muscles directly cause
a. the release of hormones.
b. the regeneration of nerves.
c. the extension of limbs.
d. the healing of wounds.

The answer is letter C.  

Muscles directly cause the movement of limbs in the body. These are mostly made up of striated tissues that slide along each other causing the movement of the whole body. These tissues are attached to the bones that make up the skeletal system. They provide the structure and frame of the body and they also serve as cushions and protection for the bones. Without muscles movement will not be possible and we would seem like hollow structures only made up of bones.

Animals will lose energy because it is converted to heat