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
Group activities will be organized after class _______ children develop team spirit.
A. helping B. having helped
C. helped D. to help
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
Today there are more airplanes________ more people than ever before in the skies.
A. carry B. carrying
C. carried D. to be carrying
______ 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
Much time _____ sitting at a desk, office workers are generally troubled by health problems.
A. being spent B. having spent
C. spent D. spending
