Note first that several months have 30 days (each): Â 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. Â If the month in question does not have 30 days, then the month could NOT be April, June or September. Â 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. Â If the month in question does NOT have 30 days, then that month could not possibly be June.