单项选择题

The problem of pollution Has been caused by several factors,（）can be kept under control.

A. most of which
B. most of them
C. most of that
D. most of what

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Henry and Jeff hadn't seen each other for two years. They greeted（）shaking hands when they met yesterday,

A. on
B. by
C. with
D. to
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You are not（）to park your car here, unless you work in this building.

A. welcomed
B. forbid
C. permitted
D. performed
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