The past perfect tense of keep is had kept.
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 submitted.
The past perfect tense is "had confronted".
Kept is the past tense of keep. The past perfect tense is had kept.
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."