Answer the following question given this paragraph: 

Segmented worms have a well-developed body cavity filled with fluid. This fluid-filled cavity serves as a hydroskeleton , a supportive structure that helps move the worm's muscles. Only the most primitive worms (the flatworms) lack a body cavity.


Q: What is the name of the supportive structed that helps move a worm's muscles?

 Choices:

- spongin

- exoskeleton

- pollenation

- hydroskeleton

A:
hydroskeleton
