in this sentence, what is the verb and label it linking or adjective:

Rennet is an extract made from the lining of a calf's fourth stomach.

I thought it would be is made and it would be action verb. My friend however thought that it was linking and that the predicate noun is extract.

Would it help if it were reworded?

Rennet, an extract, is made from ...

Sooo, wouldn't it be "is made" is the action verb

In the original sentence, your friend is right.
Rennet = subject
is = linking verb
extract = predicate noun
(made = past participle acting as an adjective modifying "extract")

=)