单项选择题

The development of the light bulb __ partly as a result of the widespread availability of electricity and the need for cheap, cicada light.

A．occurring
B．was occurring
C．was occurred
D．occurred
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单项选择题
What we have to take ______ the courses offered only for this term.
A．are
B．is
C．have been
D．has been
单项选择题
It is a small country, yet has a lot of______ resources.
A．potential
B．unknown
C．secret
D．unlimited
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