Answer:
2) Yours truly is correct.
Step-by-step explanation
Yours truly is an example of a conventional phrase that is used by a person while writing a formal e-mail or letter.
The word ' Yours in the phrase ' Yours truly ' refers to the person who is writing the letter.
The phrase ' Yours truly ' is used while writing to a person whom we have had no previous correspondence with.
Therefore the correct option will be 2) Yours truly.