单项选择题

What does the passage mainly discuss

A．The detail seen through a microscope.
B．Sources of illumination for microscopes.
C．A new kind of microscope.
D．Outdated microscopic techniques.
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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.
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
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