B13:-Ans.
He (B) must have
=we have; have---->has
=he has; has---->have
=>he hasn't been
=he hasn't been at work all week
he went on vacation
=(B)
(D) would have been to the vacation means he had not been to the vacation; which is not true ;He has been to the vacation, according to the Main Clause in the type of conditional.
(A) cannot use must go, because "he went on vacation "