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更多“knock（）”相关的问题
A.冲垮了欧洲封建统治秩序
B.推动了欧洲资产阶级革命
C.促使欧洲殖民者调整政策
D.沉重打击了欧洲封建统治者
A.“鼓帮问顶”人员要观察周围环境，严禁站在岩块下方或岩块滑落方向，并选好退路
B.必须有监护人员，监护人员应站在“敲帮问顶”人员的侧后面，并保证退路畅通
C.作业从支护完好的地点开始，由外向里、先顶后帮依次进行
D.严禁与“敲帮问顶”作业无关人员进入作业区域
A.had interrupted
B.to have interrupted
C.would have interrupted
D.to interrupt
A.were interrupted
B.was interrupting
C.had interrupted
D.had been interrupted
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
