– Can you _______ in summer ?
– Yes, I can.
A. swimming B. swim C. swimming
I must ______ the traffic lights.
A.look after B. pay attention to C. look for
Can you sing the song in English? -- No, I ____ .
A.can't B. mustn't C. needn't
What ____________ we do to protect our environment?
A. do
B. shouldn't
C. can