单项选择题

--I'd like to invite you to a concert this evening.--Thank you, but ______ I'll be free I'm not sure at that moment.

A．while
B．if
C．when
D．whether
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单项选择题
He was fired ______ his carelessness and laziness.
A．because of
B．because
C．thanks to
D．since
单项选择题
On ______ the notes proved to be forgeries.
A．inspect
B．inspection
C．inspector
D．inspecting
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