Note first that several months have 30 days (each): April, June and September.
(A) could not be correct, since the month in question could have 28, 29 or 31 days.
(B) See (A), above. If the month in question does not have 30 days, then the month could NOT be April, June or September. Reject (B).
(C) You do this one, similarly to my responses to (A) and (B), above.
(D) This one is true, since we know that June has 30 days. If the month in question does NOT have 30 days, then that month could not possibly be June.