单项选择题

Which is the best title for the passage

A．Scientists Created X-rays in a Lab.
B．Sparks, a New Way to Produce X-rays.
C．Runaway Breakdown Triggers New Questions.
D．Scientists Surprised by X-rays from Lab Lightning.
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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.
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
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