单项选择题

(That) the sun (but) not the earth (is) the center of our planetary system (was) a difficult concept to grasp in the Middle Ages.

A．That
B．but
C．is
D．was
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单项选择题
She ought (to) (stopping) work; She (has a headache )because she has been reading (too) long.
A．to
B．stopping
C．has a headache
D．too
单项选择题
The growth (of) part-time and flexible working patterns (allow) more women (to) (take) advantage of employment opportunities.
A．of
B．allow
C．to
D．take
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