单项选择题

Only recently ______ possible to separate the components of fragrant substances and to determine their chemical composition.

A．it becomes
B．having become
C．has it become
D．which becomes
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The man was detained by the police at the airport because his passport was found to be ______.
A．an artificial one
B．an unnatural one
C．an untrue one
D．a false one
单项选择题
Jacobson is often referred to ______ at the factory.
A．as the best engineer
B．be the best engineer
C．by the president to be best engineer
D．as being the best engineer
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