Identify perfect tense verbs

The perfect tenses describe actions in relation to another point in time, and they all use a form of "have" plus a past participle.

The present perfect uses has or have plus a past participle.
It describes an action that began in the past and still matters or continues now.
For example, "Leonardo's fame has remained undimmed to this day" shows that the fame started long ago and lasts into the present.

The past perfect uses had plus a past participle.
It marks an action that was already finished before another past action happened.
For example, "By the time the Renaissance began, feudal lords had ruled the land for centuries" shows the ruling came before the Renaissance.

So pick the tense that fits the timeline of the sentence.
If the sentence is about something that continues into the present, use the present perfect.
If it describes an earlier event within a past story, use the past perfect.

Leonardo da Vinci's fame, filtered through centuries of criticism, ______ undimmed to the present day.
Which choice correctly completes the sentence?
(A) has remained
(B) remained
The fame began in the past and continues right up to now, which calls for the present perfect.
So (A) "has remained" is correct.

By the time the Renaissance reshaped Europe, powerful feudal lords ______ the countryside for many centuries.
Which choice correctly completes the sentence?
(A) had ruled
(B) rule
The ruling happened before the past event of the Renaissance, which calls for the past perfect.
So (A) "had ruled" is correct.

Marine biologists ______ these deep-sea creatures for decades, and they are still studying them today.
Which choice correctly completes the sentence?
(A) have studied
(B) studied
The studying started in the past and continues into the present, which calls for the present perfect.
So (A) "have studied" is correct.