[单项选择]By moving the radar beam around slowly in circles, we can ______ the surroundings.
A. explore
B. expose
C. exploit
D. expand

[单项选择]By moving the radar beam around slowly in circles, we can ______ the surroundings.
A. explore
B. expose
C. exploit
D. expand

[单项选择]Telephones develop very slowly.

[单项选择]Laser-doppler radar is especially valuable in space missions because ______. ( )
A. it is one thousand times more precise than microwave radar
B. it provides precise measures of the velocity of space vehicles
C. it is a new system of radar
D. it can measure the movement of a spaceship less accurately than a microwave radar

[单项选择]The installation of radar is supposed to keep track of airlines in the __________.
A. velocity
B. proximity
C. terrain
D. vicinity

[单项选择]Laser-dopple radar is especially valuable in space missions because it ______.
A. is one thousand times more precise than microwave radar
B. provides precise measures of the velocity of space vehicles
C. is a new system of radar
D. can measure the movement of a spaceship less accurately than a microwave radar

[单项选择]

Passage Five
A new kind of radar has been developed for spaceship travelers. A working laboratory model of a new system of radar that makes use of a beam of light is said to be ten thousand times more accurate than the best comparable system of radar that used microwaves.
The model has shown that this radar system, known as laser-doppler radar, can measure with absolute precision speeds varying from spaceship orbital injection (进入) velocities (速度) of five miles per second down to virtual stops--speeds of less than one ten thousandth of an inch per second. According to the scientists who are developing this system, such fine measures of velocity are of prime importance in space missions. In a rendezvous (对接) between two spaceships, or in a landing approach by a vehicle onto an orbiting space station, a bump could rip open a ship’s skin, or a nudge could knock the station out of its orbit.
The light-beam radar, which operates at a frequency of t
A. laser-doppler radar is more accurate than microwave radar
B. microwave radar may not ensure absolute precision in measuring varying speeds
C. the light-beam radar can measure only slow speeds with accuracy
D. microwave radar operates at a higher frequency than laser-doppler radar

[单项选择]According to the passage, slowly rising birthrate perhaps is good for ______.
A. a developed nation
B. every nation with a high population
C. a developing nation
D. every nation with a small population

[单项选择]Without the radar receiver, the large antenna(无线) ______ of no use.
A. would be
B. will be
C. be
D. was

[单项选择]Laser-dopple radar ______.
A. measures the movement of a spaceship by means of light beam
B. makes use of microwaves
C. makes use of sound waves
D. both A and B