Question

it must have been he who has sent this email ____mark​

Answer 1

have been is the correct answer

Answer 2

The correct answer is 'to'.

It must have been he who has sent this email to Mark.

• the word 'to' is used in the above sentence as a preposition.
• a preposition is a word used before a noun pronoun or a noun phrase to show location, time, spatial relationship, direction, or to introduce an object.
• Examples of prepositions are to, on, in, at, under, etc.