When we were in London we visited ...... National Gallery.

Semiconductor memories appear to be ...... expensive among the other memories.

The people of this country.

Rapid changes ...... place in science since the end of the 19 century.

If there ....... strangers in space, astronomers would see them through telescopes.

The scientists of our Institute ...... at this problem for two years.

Plastic is ...... material of three materials: metal, rubber, plastic.

...... Historian is a person who studies history.

...... the force applied and distance moved ...... work have been performed.

The instruments of his father.