单项选择题

Stewart found certain plant juices were useful in his experiments when he ______.

A．realized they gave off gas fumes
B．saw they contained electricity
C．noticed their effect on his skin
D．discovered their secret names
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单项选择题
Steward sent his research to various agencies just because ______.
A．he wanted to become a university professor
B．he sought to get official recognition and acceptance
C．he hoped the Army could use it in military warfare
D．he hoped the government would invest money in the project
单项选择题
Why will battery buses cost less than conventional buses in the long run
A．They will spread the capital cost over a long period.
B．They will be stronger and last longer.
C．They will use less fuel and cost less to maintain.
D．They will be charged at night when electricity costs less.
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