First, the movement of animals does not necessarily involve the participation of the movement system. For example, earthworms do not have a movement system, and the error is great.

B, some animals exercise without the participation of bones, such as earthworms, correct.

C. When the skeletal muscle is contracted by nerve stimulation, it will affect the movement of the bones around the joints, so the body will move, correct.

D, animal behavior is often manifested in various actions. The movement of animals depends on a specific body structure. Correct.

So choose: a