Much time _____ sitting at a desk, office workers are generally troubled by health problems.

A. being spent B. having spent

C. spent D. spending

______ the difference between the two research findings will be one of the worst mistakes you make.

A. Ignore B. Ignoring

C. Ignored D. Having ignored

Today there are more airplanes________ more people than ever before in the skies.

A. carry B. carrying

C. carried D. to be carrying

The producer comes regularly to collect the cameras _______ to our shop for quality problems.

A. returning B. returned

C. to return D. to be returned

Group activities will be organized after class _______ children develop team spirit.

A. helping B. having helped

C. helped D. to help

There are still many problems ______ before we are ready for a long stay on the Moon.

A. solving B. solved

C. being solved D.to be solved

Last night, there were millions of people _______ the opening ceremony live on TV.

A.watch B. to watch

C. watched D. watching

Clearly and thoughtfully________, the book inspires confidence in students who wish to seek their own answers.

A. writing B. to write

C. written D. being written

There is a note pinned to the door______ when the shop will open again.

A. saying B. says

C. said D. having said

When it comes to __ in public, no one can match him.

A. speak B. speaking

C. being spoken D. be spoken