It _______ long before we _________ the result of the experiment.

[　　]

A．will not be; will know

B．is; will know

C．will not be; know

D．is; know

Professor Wang walked onto the platform and took his seat, _______ to answer questions.

[　　]

Children at the beginning of this century ______ a lot and ______ themselves greatly even without television.

[　　]

This machine _______.It hasn't worked for years.

[　　]

What is the way Tom thought of _______ enough money to buy a car?

[　　]

Many _______ has been sent out to scientists from different fields.

[　　]

More than one _______ for the 1 000-meter race to be held next week.

[　　]

If city noises ________ from increasing, people ________ shout to be heard even at the dinner table 20 years from now.

[　　]

All the people must stop pollution ________ our city cleaner and more beautiful.

[　　]

The soldiers on duty take turns _______ at night.

[　　]

A．keeping watch

B．of keeping watch

C．to keep watch

D．kept watch