Anoun that completes an action is called a/an a. complement. b. object. c. predicate. d. subject.

A. Compliment   

An object is a noun that receives the action of the verb.  A subject is the doer of the verb.  And, a predicate completes the sentence; though this, too, can be a noun, a predicate noun completes the sentence, not the action. A noun that completes an action is the compliment.  This does not mean, however, that other parts of speech cannot function as a compliment.  A compliment can really be any word or words (phrase) that completes an action. 

 The correct answer is : A. complement

Explanation:  Syntactically, nouns can function as arguments of the verb. The noun can be a complement to the verb. Some verbal supplements may be mandatory and others serve to add information.

the third one.

hope it

faith or loyalty when pledged in a solemn agreement or undertaking.