单项选择题
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
A．accuracy ill speed measurement is essential to spaceships B．the speeds of space vehicles will vary C．inaccuracies in measurement could cause accidents in space missions D．a bump could affect the preciseness of the laser-doppler radar
A．Henry Ford always tried to avoid waste B．Henry Ford required total observation once the standards were established C．Henry Ford always encouraged his workers to make changes oft he products D．Henry Ford made his own designs of his cars