The reason why he was late is ______ he got up too late.

We are _________ by doctors to eat more natural food and take plenty of physical exercise.

Must I finish that work today?—-No, you _____. You may finish it in three days.

You should study _____ a test _____ reading the textbook. [ ]

Qinghai-Tibet Railway(青藏铁路) was completed last year. It is the __________ railway that connects Tibet with the other parts of China.