Q: Which has a unique water vascular system?
Options:
- (A) roots
- (B) trees
- (C) Conifers
- (D) Echinoids
- (E) fur seals
- (F) Most plants
- (G) ferns
- (H) bushes
Let's think step by step below.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Echinoderms have a unique water vascular system with tube feet. Another group of echinoderms are the echinoids. Echinoids have unique water vascular system was tube feet.
Thus, the answer is (D).