(fail) several times, they need some encouragement.

The floor does not look so bad when(sweep) clean. 

Some molecules are large enough(see) under the electronic microscope.

We were busy(get) things ready for the trial production when he phoned us.

A beam of light will not bend round corners unless(make) to do so with the help of a reflecting device

Night(fall), we hurried home.

I wonder if he could get it(do) before tomorrow.

I shall never forget(meet) the late Premier Zhou during his inspection of our factory.

Matter is the name(give) to everything which has weight and occupies space.

He refused to tell us whether he(undertake) the job.