单项选择题

The tendency of the human body to reject foreign matter is the main obstacle to successful organ transplantation.

A．factor
B．constituent
C．barrier
D．break
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单项选择题
The world economic recession put an ______ end to the steel market upturn that began in 2002.
A．irregular
B．illegal
C．abrupt
D．absurd
单项选择题
It ______ without saying that consumers would be happier if prices were lower.
A．takes
B．appears
C．makes
D．goes
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