单项选择题
A．a great deal of B．a lot C．a number of D．a bit of
A．accuracy in 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．has a great deal of trouble doing mental arithmetic B．lacks some of the qualities required of a scientist C．just reads about other people’s observations and discoveries D．comes up with solutions in a most natural way