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.
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).