PASSENGERS _______ SMOKE UNTIL THE SIGNS HAVE BEEN SWITCHED OFF. A...
13. Passengers _______ smoke until the signs have been switched off.
A. mustn't
B. can't
C. needn't
D. mightn't
13. Passengers _______ smoke until the signs have been switched off.
A. mustn't
B. can't
C. needn't
D. mightn't