单项选择题

You must be very careful when handling these acids______they are very concentrated.
A．as
B．when
C．if
D．while

A.
A．as
B．when
C．if
D．while

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单项选择题

______he starts a job, he won't stop until it is finished.
A．Once
B．After
C．Until
D．As soon as

A.
A．Once
B．After
C．Until
D．As

单项选择题

We got wet in the rain______none of us had brought along a raincoat.
A．so
B．because
C．in order that
D．when

A.
A．so
B．because
C．in
B.when