赞题库-背景图

单项选择题

The estimate is based on the______.

A．direction of the hill
B．accepted speed of sound
C．interval between sound and echo
D．both B and C

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热门试题

单项选择题Radar enabled the English ______.

A．detect German planes on their way to London
B．direct the outnumbered RAF planes effectively
C．confuse German bomber pilots
D．both A and B

单项选择题Practical application of this principle resulted in ______.

A．new electronic instruments for planes
B．new radio sets for RAF bombers
C．an electronic detecting device
D．a radio directing and ranging device