单项选择题

______ with air, a life jacket will keep a person afloat.

A．It is filled
B．Filling
C．When filled
D．When filling it
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单项选择题
Indigo is a vat color,______ called because it does not dissolve in water.
A．which it
B．it is
C．but
D．so
单项选择题
The king's daughter threatened to drink the ______ chemical if he refused her request.
A．deathly
B．deadly
C．fatal
D．mortal
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