单项选择题

Which of the following statements is true according to the passage

A．All the researchers doubt that X-rays can be produced by sparks at first.
B．X-rays produced in lab is just the same with those by lightning.
C．The result of the study is in expectation of every researcher.
D．The researchers detected X-rays in sparks of 1.5 million to 2 million volts.
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单项选择题
According to the passage, scientists used to think that the X-rays were produced by ______.
A．making sparks in laboratory
B．discharges of high-energy electron in the Sun, in exploding stars, and in lightning
C．electrons escaping their normal connections
D．radio waves
单项选择题
What does the word generating mean in paragraph five
A．It means "creating".
B．It means "producing".
C．It means "inventing".
D．It means "doing".
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