单项选择题

Why does the author mention the visible-light microscope in the first paragraph

A．To begin a discussion, of sixteenth-century discoveries.
B．To put the X-ray microscope in a historical perspective.
C．To show how limited its uses are.
D．To explain how it functioned.
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单项选择题
According to the passage, the invention of the visible - light microscope allowed scientists to ______.
A．see viruses directly
B．develop the electron microscope later on
C．understand more about the distribution of the chemical elements
D．discover single-celled plants anal animals they had never seen before
单项选择题
Which of the following is NOT mentioned when the author explains the reasons of the rapid growing number of English speaker
A．New pupils are required to learn English at school.
B．Monolingual old people are encouraged to speak English.
C．Employees have to learn English if they want to get a chance of promotion.
D．Scholars use English as the language of their academic works more often than other languages.
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