单项选择题

We must be ______ our guard against this kind of disease.

A．on
B．in
C．with
D．for
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单项选择题
Mum wants to tell her boys ______.
A．how difficult it is to raise them
B．how difficult is it to raise them
C．how difficult to raise them
D．how difficult is to raise them
单项选择题
Many a girl ______ dancing and singing at the center of the stadium.
A．are
B．is
C．be
D．am
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