We need clear air and water, so we _____ protect the environment.

You look so tired.—My mother makes me ______ playing the piano for 2 hours every day.

Hello, Betty! Where are you now — I ________ on the Great Wall of China and talking toyou.

velopment of industry has been ____gradual process throughout _____ human existence, from stone tools to modern technology.

__________? —OK. I’d like beef and carrot noodles.