【正文】
( )1. London is a big city ___________ dirty air. A. on B. for C. with ( )2. It ________ dirty before, but it _________ clean now.\ A. is is B. is was C. was is ( )3. Listen! Someone _________ the violin. A. is playing B. plays C. playing ( )4. What’s your bedroom __________ today? A.