Had applauded.
The past tense is applauded.
The present perfect tense of applaud is:I/You/We/They have applauded.He/She/It has applauded.
The present perfect tense of applaud is:I/You/We/They have applauded.He/She/It has applauded.
The word applause is a noun and so doesn't have a past tense. The past tense of the verb applaud is applauded.
Laud means to praise. But applaud means to clap in approval. It specifically means clapping.
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.