Given a scientific question, generate a correct answer to it.

[EX Q]: Herbivores are heterotrophs that eat only or mainly what?
[EX A]: plants

[EX Q]: What term refers to the sequence of community and ecosystem changes after a disturbance?
[EX A]: ecological succession

[EX Q]: What guards the opening between the right atrium and the right ventricle?
[EX A]:
tricuspid valve