What does the passage mainly discuss? Why did it take so long to develop the X-ray microscope?

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问题 What does the passage mainly discuss?
Why did it take so long to develop the X-ray microscope?

选项 A、Funds for research were insufficient.
B、The source of illumination was not bright enough until recently.
C、Materials used to manufacture X-ray tubes were difficult to obtain.
D、X-ray microscopes were too complicated to operate.

答案B

解析 本题考查对文章细节部分理解的能力。文章第二段详细介绍了X射线显微镜为什么经过那样长时间才得到发展。文章谈到,在四十年代,电子显微镜由于其分辨率大大提高而得到很大的发展,但X射线显微镜却因为没有任何改进而停滞不前。近几年,X射线显微镜得到关注大部分是因为"the development of new sources of X-ray illumination"这种采用新的照明源的X射线显微镜没得到发展是因为照明源的亮度不够。
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