ou are a difficult period,it often helps to talk to someone.

Do you know where the headmaster is? I have something urgent.—Oh, he ______ have gone far, for the computer is still on in the office.[ ]

We are now living in a high-tech age ____ easy things are becoming complicated．

Scientists estimate that plants and animals lived _____ 3.5 billion years ago[ ]

The students will take morning exercise every day, _________ it rains