A new kind of radar has been developed for space-age 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 uses 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 velocities(對(duì)接速度) 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 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 slight push could knock the station out of its orbit. The light-beam radar, which operates at a frequency of trillions of cycles per second, could easily detect and measure the movement of a vehicle edging up to a satellite space station even at a small fraction of an inch per second. A country system using so precise a signal as this would allow a huge vehicle to dock at a space station as lightly as a feather.

11. Laser-doppler radar makes use of _____.

(A) microwaves

(B) light

(C) sound waves

(D) both A and B

2. This radar system is significant because it _____.

(A) is the first radar system to work in space

(B) is more precise than microwave radar

(C) is easiest to operate than microwave radar

(D) will work on the earth´s surface as well as in space

3. Precision in measuring slow speeds will help space pilots to _____.

(A) attain orbital injection velocities

(B) manned rendezvous in space

(C) land at space station

(D) both B and C

4. The ability of laser-Doppler radar to detect and measure low speeds comes from its _____.

(A) operating at a high frequency

(B) operating at a low frequency

(C) being more precise than microwave radar

(D) not being affected by the size of an object

5. Implied but not stated _____.

(A) Laser-Doppler radar is more accurate than microwave radar.

(B) Microwave radar does not insure absolute precision in measuring varying speeds.

(C) The light-beam radar can measure only slow speeds with absolute accuracy.

(D) Microwave radar operates at a ligher frequency than laser-Dopple radar.

答案：B B D A B