The past perfect tense of fail is had failed.
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".
The past tense of fail is failed, the present tense of fail is fail, and the future tense of fail is to fail or going to fail.
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 of hope is had hoped.
The past perfect tense is had submitted.
The past perfect tense is had chosen.
The past perfect tense is "had confronted".
The past perfect tense is had set.
The past perfect tense is had burned.
The past perfect tense is had rung.
The past perfect tense of "learn" is "had learned."