Immediately before going out of the spaceship,the astronauts have to__________ .
A.check the spaceship doors
B.walk through the bellows
C.attach each other with a cable
D.do some warm.up exercises
The main idea of the whole story is that ______ .
A.there is more food and water in space than on earth
B.eating and drinking in space is a special problem
C.astronauts can never eat or drink in a spaceship
D.there is no food or water in a spaceship
A.装载物品不符合装载规定
B.车辆存在严重故障隐患
C.工作疲劳、身体不适或正在患妨碍安全驾驶的疾病
D.其他违章驾驶指令
A.禁止边开车边使用手机等影响驾驶的不安全行为
B.在临时上下车地点上下车,注意过往行人/车辆
C.经人行道时,确认安全,后通过
D.喝酒照样开车,怕过谁
The story does not say this, but from what we have read, we can tell that ______ .
A.you get much hungrier in space than you do on the earth
B.you can't have water to drink in a spaceship
C.astronauts must learn many new and different things
D.you can't eat anything in a spaceship
The writer advises us to think about ecology, because ______.
A.it enables us to survive in the closed system of a spaceship
B.it is a modern science that everybody has to learn
C.it can be learned quickly if we study it hard
D.it helps us to understand the relationship between living beings and the environment
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 trillions (百万兆) of cycles per second, could easily detect and measure the movement of a vehicle edging up to a satellite space station. A control system using so precise a signal as this would allow a huge vehicle to dock at a space station as lightly as a feather.
Laser-doppler radar ______. ()
A.measures the movements of a spaceship by means of light beam
B.makes use of microwaves
C.makes use of sound waves
D.Both A and B
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