From the context of the sentence stem, you'll have to decide which form works best in the sentence. Used alone, an infinitive, gerund, or participle cannot be amain verb.
The verb is active, but it should be passive, or it is passive but it should be active.
If the subject of the sentence performs the action, the verb must be in the active voice. If the subject ofthe sentence receives the action, the verb must be in the passive.
· The architect designed the building, (active verb).
· The building was designed by the architect, (passive verb).
The verb does not agree with its subject.Singular subjects require singular verbs; plural subjects require plural verbs.
The verb is not in the right tense.According tothe time words or ideas in the sentence, the appropriate tense must be used.
An unnecessary element comes before the verb.Personal pronouns {he, she, it), relative pronouns {who, which, that, and so on), or conjunctions (and, but, and so on) may be used unnecessarily before verbs in some sentences.
Example
Before the late eighteenth century, most textiles _____ at home.
(A) produced
(B) was produced
(C) producing
(D) were produced
Choice (D) is the best answer. (A) can be considered either an active verb in the past tense or a past participle; both are incorrect. An active verb is incorrect because a passive verb is needed; a past participle is incorrect because a past participle cannot serve as a main verb. (B) is incorrect because the plural subject textiles requires a plural verb, were. (C) is incorrect because, by itself, an -ing form can never be a main verb.