单项选择题

Although we are (concerned with) the problem of energy sources, we (must not) fail (recognizing) the need (for) environmental protection.

A. concerned with
B. must not
C. recognizing
D. for
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(Historically) (there) (has been) (only) two major factions(部分) in the Republican Party -- the liberals and the conservatives.
A. Historically
B. there
C. has been
D. only
单项选择题
(The Chinese) were the first and (large) ethnic(种族) group (to work) on the construction (of) the transcontinental railroad system.
A. The Chinese
B. large
C. to work
D. of
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