一Climate change________mainly by too much CO 2 in the air.一So I think the key is to produce electricity without creating CO2A.is caused B.caused C.causes
With these words, she ________ her face with her hands. She felt shy.
It is getting warmer and warmer. You ________ wear so many clothes.
—Where are your children? —I had no idea. But when I left home this morning, I saw them _______ a football in the yard.
Don’t ________ until the bus stops. Or it’s too dangerous.
Mr. Smith was ill ________. He had to have three weeks ________.