9. What is a linking verb?
a word that tells what someone or something is doing
a word that is added to another verb to make a verb phrase
a word that describes a person, place, or thing
a word that helps one word in a sentence name or describe another word in the sentence

A word that helps one word in a sentence name or describe another word in the sentence.

Explanation:

Linking verbs serve two purposes. First, they serve to help rename or re-identify the subject. For example,

He is a musician.  

The linking verb is connects the subject he with the noun musician. In other words, the linking verb is helps one word in a sentence (musician) rename  another word in the sentence (he).

Second, linking verbs serve to help describe the subject. For example,

They are huge.

The linking verb are connects the subject they with the adjective huge. In other words, the linking verb are helps one word in a sentence (huge)  describe another word in the sentence (they).

your awnser would be b.