单项选择题

Among the many open research questions on MTBE are how it is metabolized, ______the levels of exposure in the general population are.

A．but what
B．and what
C．but how
D．and why
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单项选择题
If the additives are ______, the University of California researchers recommended caution in approving any alternatives.
A．postponed up
B．phased up
C．phrased up
D．phased out
单项选择题
Based on their review, the University of California researchers concluded that MTBE is an animal virus ______ cause cancer in humans.
A．without doubt to
B．without question to
C．with the intention to
D．with the potential to
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