He transplanted the young tree to the park ____ it was the best time for it .
| A．where | B．when | C．what | D．that |
Not until I came home last night ________ to bed.
| A．Mum did go | B．did Mum go | C．went Mum | D．Mum went |
Work hard when young, ______ you will regret.
| A．and | B．so | C．but | D．or |
It’s hot in the shopping mall, because the air-conditioning system ______.
| A．broke up | B．broke down | C．broke in | D．broke out |
--- It’s the fourth time that heavy smog(雾霾) has hit the city this month.
--- It’s high time we _______ measures to fight air pollution.
| A．will take | B．took | C．to take | D．taking |
Science has given clear evidence ______ smoking can lead to many diseases.
| A．what | B．which | C．that | D．where |