1 . We should protect the environment. We should not cut down the trees. (两句合一句)
We should protect the environment by ________ ________ down the trees.

2 . I’ve bought many bells. They are used for _______ the Christmas tree.

A．decorate

B．to decorate

C．decorating

D．decorated

3 . We should often review our notes after class to avoid ________ the same mistakes.

A．make

B．to make

C．made

D．making

4 . The professor suggested that the students consider ________ more research on the topic.

A．do

B．doing

C．to do

D．done

5 . Sara is used to ________ a glass of water when she gets up in the morning.

A．drink

B．drinks

C．drinking

D．drank

6 . When the police asked the doorkeeper about the theft, he denied ________ any stranger.

A．to see

B．seeing

C．see

D．saw

7 . Every time I pass by her office, she’s busy __________ something.

A．do

B．to do

C．done

D．doing

8 . Citizens in modern cities should consider ________ electric cars instead of fuel cars when going to work every day.

A．use

B．to use

C．using

D．used

9 . You should avoid ________ on the underground. It’s impolite and also against the rules.

A．eat

B．eating

C．ate

D．to eat

10 . As a lover of Chinese culture, Tina keeps         videos to learn about real life in China.

A．watch

B．watching

C．to watch

D．watched