单项选择题

What is the author's main purpose in writing this passage

A．Emphasizing the importance of protection from radiation.
B．Solving the mystery about radiation.
C．Discussing the cause of cancer.
D．Introducing the nuclear power.

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单项选择题

What can we infer from the passage

A．We can't detect radioactivity even with modern equipment.
B．Only radiation at very high levels can kill an animal or human being.
C．If a few cells are only damaged, healthy cells will take the place of dead ones.
D．Radiation is harmful no matter what level it is.

单项选择题

The word significant in Paragraph 3 has the similar meaning with ______.

A．fatal
B．meaningful
C．harmful
D．remarkable