单项选择题

The doctor will not perform the operation______it is absolutely necessary.

A. so
B. if

C. for
D. unless
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单项选择题
The author’s intention in writing the passage is to().

A. praise the wisdom of the old people
B. advise people to be patient
C. analyze the danger of heart diseases
D. persuade people to be trustful
单项选择题
The cure for lung cancer ().

A. can be found before long
B. is available if one needs it
C. is unknown at present
D. will be found before you need it
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