Answer: C. the circular muscles
Explanation:
In earthworm the circular muscles will help in extension and elongation of the worm. This helps to extend the front part of the earthworm and also guides to move in the direction where the front part or head moves. The earthworm body is made up of many ring like segments each segment is made up of circular muscles which helps in movement. When these circular muscle contracts, the earthworm stretches and becomes thinner and longer.
