单项选择题

A．The high temperatures required for its use.
B．The lack of trained environmental engineers.
C．The opposition of automobile manufacturers.
D．The high cost of materials used in its production.
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单项选择题
A．Its chemical elements must be studied.B．Its temperature must be lowered.C．Big spaceships must be built.D．Its atmosphere must be changed.
A．Its chemical elements must be studied.
B．Its temperature must be lowered.
C．Big spaceships must be built.
D．Its atmosphere must be changed.
单项选择题
A．He plans to sell the books to a collector.B．The old books are worth a lot to collectors.C．He won’t sell the books until he has read them.D．The books probably aren’t worth much in terms of money.
A．He plans to sell the books to a collector.
B．The old books are worth a lot to collectors.
C．He won’t sell the books until he has read them.
D．The books probably aren’t worth much in terms of money.
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