What tense is this verb ?
The state police were pulling over many drivers? I think its past progressive but i don't know if it would also be considered past perfect progressive.
what principle part is used to form the verb in each sentence?
1.The workers will have finished by now.
2.Detectives had been investigating for months/
Past progressive is correct for the verb in the first sentence.
What do you think about the principle parts in the other two sentences?
To determine the tense of a verb, it's important to identify both the auxiliary verb and the main verb in the sentence. In the sentence "The state police were pulling over many drivers," the auxiliary verb is "were" and the main verb is "pulling."
The verb tense in this sentence is past progressive. The past progressive tense is formed by using the past tense of the auxiliary verb "to be" (in this case, "were") combined with the present participle of the main verb ("pulling").
Regarding your question about whether it could be considered past perfect progressive, the past perfect progressive tense is formed by using the past participle of the auxiliary verb "to have" with the auxiliary verb "to be" in the past participle form (e.g., "had been"), followed by the present participle of the main verb. Since the sentence does not contain the auxiliary verb "had" in addition to "were," it is not in the past perfect progressive tense.