Answer:
The main verb in the sentence above is passive.
Explanation:
In most English sentences with an action verb, the subject perfoms the action denoted by the verb. Because the subject does or acts upon the verb in such sentences, the sentences are said to be in the active voice. However, it is possible to change the order of the words in many active sentences so that the subject is no longer active, but being acted upon by the verb or passive. In order to create a passive construction, you should first move the active sentence's direct object into the subject position, and then you can place the active sentence's subject in a by-phrase (by the chimpanzees).
