Read, then choose the best answer by circling the corresponding letter A, B, C or D.
Radar is an electronic device that can "see" great distances (1)...... fog, rain, snow, cloud, and darkness. It can find and (2) locate missiles, aircraft, ships, cities, rainstorms, and mountains. Radar uses radio waves, (3)........... light waves, which the human eye uses in seeing. This makes it (4)........ for radar to locate many kinds of objects at (5)....... greater distances than the eye can see. Radar became an important military device during World War 11. Today, networks of radar lookout stations guard the United States and Canada 24 hours a day against (6)....... missiles and airplanes. Patrol planes and ships (7)........ the oceans with radar for hostile Ships and aircraft. Airports use radar to (8)........ planes safety to earth in fog or storms. Ships use it to steer clear of other (9)......... or icebergs. Radar helps Weathermen warn of (l 0) hurricanes or tornadoes.
Trả lời câu hỏi dưới đây:
(1)..........