单项选择题

(The age of) a geological sample can (be estimated) from the ratio of radioactive to nonradioactive carbon (present) in the object (is examined).

A. The age of
B. be estimated
C. present
D. is examined
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单项选择题
(No wonder) that (man’s) great dream has been someday to control the weather. The first step toward control is knowledge, and scientists have been (hard at work) for years trying to (keep track for) the weather.
A. No wonder
B. man’s
C. hard at work
D. keep track for
单项选择题
The author argues that a teacher’s chief concern should be the development of the student’s ______ .
A．personal qualities and social skills
B．total personality
C．learning ability and communicative skills
D．intellectual ability
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