I won’t tell the student the answer to the math problem until he ________ on it for more than an hour.
| A．has been working | B．will have worked | C．will have been working | D．had worked |
_____, water can be changed into gas.
| A．Heated | B．Being heated |
| C．Having heated | D．Having been heated |
There is _____ what the weather will be like.
| A．not knowing | B．no knowing | C．not know | D．no known |
I am too glad _____ you.
| A．to see | B．seeing | C．saw | D．at seeing |
The Arctic is considered _____ the northern part of the Atlantic.
| A．having been | B．to have been | C．to be | D．being |
_____, the boy couldn't enter his house.
| A．Since the key had lost | B．The key being lost |
| C．Lost the key | D．Having lost the key |