Who asked you to draft this letter?

By whom were you asked to draft this letter?

By whom are you asked to draft this letter?

By whom will you asked to draft this letter?

By whom should you asked to draft this letter?

All of the above

This is an interrogative sentence of Past Indefinite Tense.

Past Indefinite tense

Active Voice= Subject + Second Form of Verb + Object.

Passive Voice = Object + was/were + third of verb + by + subject.