单项选择题

______is our duty______ good service to customers.

A．That, to give
B．This, giving
C．It, to give
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单项选择题
Joy was sad because his pet cat______.
A．was died
B．had been dead
C．had died
单项选择题
Nobody should______.
A．laugh at
B．be laughed
C．be laughed at
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