Read the sentence that is being evaluated carefully. Find the action of the sentence. Verbs express actions, events or states of being. For example, in the sentence "He lives in London," the verb is "lives" because it is an action that "he" is doing.
Look for phrases of action. Once you find the main verb in the sentence, look to see if the preceding word is also a verb. A verb string consists of up to four verbs that precede the main verb in a sequence. The first verb in a string is called the finite verb, and the word before the main verb is called the auxiliary verb. The main verb of the string is the final word in the sequence.
Identify verb strings by phrases that express variations in time or mood. In the sentence "We have been looking for John for more than 30 minutes," the verb string is "have been waiting." The verb "have" is the finite verb, and "been" is the auxiliary verb. "Waiting" is the main verb because it is the last word in the action phrase.