Answer:
A. Skeletal muscles
Explanation:
An effector is a group of cells, an organ, gland or any part of the body that acts to bring about a change in response to a nerve impulse from the CNS.
In the case of thermogenesis as stated in the question above, where a drop in temperature is detected by thermoreceptors in the CNS, the part of the body that responds in returning the body temperature back to its baseline are the skeletal muscles. The skeletal muscles are the effectors that responded in repeated contracions to generate heat.
