—Why do you look so puzzled?
—Oh，I ________ over a most difficult maths problem.
| A．thought | B．have thought |
| C．am thinking | D．think |
Since then the number of people taking driving lessons ________ 20％.
| A．has increased to | B．increases by | C．has increased by | D．have increased by |
To understand the grammar of the sentence, you must break it ____ into parts.
| A．down | B．up | C．off | D．out |
The whole class________ the teacher attentively.
| A．are listening to | B．is listening to |
| C．are listening | D．is listening |
We don’t allow ____ in the office. But you are allowed ______ in the open air.
| A．smoking; smoking | B．to smoke; to smoke |
| C．smoking; to smoke | D．smoke; smoking |
What ____ fun it is to walk alone with ______ full moon hanging in the sky.
| A．/; a | B．a; / | C．the; / | D．a ;the |