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单项选择题

The practical use of radio waves brought about______.

A．new machines for planes
B．a radio directing and ranging device
C．new radio sets for RAF bombers
D．a discovering device

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热门试题

单项选择题Sound waves reflected from a hill can be used to calculate the______.

A．Speed of sound
B．time between a sound and ifs echo
C．height of the hill
D．distance of the hill

单项选择题What was the speaker's purpose in sharing the story about his grandfather

A．To highlight the difficulties of finding affordable housing in the future.
B．To illustrate older people's loss of identity and self-worth.
C．To describe the lack of public facilities designed for the elderly.
D．To justify that self-worth is often tied to one's profession and social standing.