1. The guests at the party were dancing to _______ music when all of _______ sudden all the lights went off.
A. /; / B. a; a C. the; / D. the; a
2. — Is the table by the window _______?
— Sorry, sir. It’s been booked already.
A. free B. blank C. vacant D. convenient
3. A clean environment needs everyone’s efforts and _______, we should make a contribution to it.
A. however B. therefore C. besides D. instead
