Your pronunciation needs ________.

[　　]

Students should do everything they can ________ their study.

A．improve           B．to improve             C．improving               D．improved

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—Why did you plant so many trees?
— ______ the environment.

—Why did you plant so many trees?

— ______ the environment.

A．Improve

B．To Improve

C．Improved

D．Improving