I had studied.
The past perfect is formed with - havd +past participle.
The past participle of study is studied
Studied is the past tense of study.
Existed is the past tense. The past perfect tense is had existed.
The past tense is bled, and the past perfect tense is had bled.
The past tense of sit is sat; the past perfect tense is had sat.
The past perfect tense is "had confronted".
Studied is the past tense of study.
Existed is the past tense. The past perfect tense is had existed.
The past tense is bled, and the past perfect tense is had bled.
The past tense of sit is sat; the past perfect tense is had sat.
The past perfect tense is "had confronted".
The past perfect tense is had chosen.
The past perfect tense is had burned.
The past perfect tense is had set.
The past perfect tense is had rung.
The past perfect tense of hope is had hoped.
The past perfect tense is had submitted.
The past perfect tense of "learn" is "had learned."