The answer is A and that’s all you need to know.
I believe that the message the author is trying to convey in this excerpt is that humans need to take action to end further destruction of the natural environment, because if they don't, more and more species will disappear.
A predicate nominative is a word or word group that is in the predicate and that identifies the subject or refers to it. A predicate nominative appears only in a sentence that has a linking verb. Common linking verbs include is, was, will be, has been, and could have been.
It is C.
Volunteer is a predicate nominative.
<em>Hope this helps!</em>
