单项选择题

A．A fuel that burns cleanly.
B．An oil additive that helps cool engines.
C．A material from which filters are made.
D．An insulating material sprayed on engine parts.
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单项选择题
A．Because people might have to migrate there someday.B．Because it is very much like the earth.C．Because it is easier to explore than other planets.D．Because its atmosphere is different from that of the earth.
A．Because people might have to migrate there someday.
B．Because it is very much like the earth.
C．Because it is easier to explore than other planets.
D．Because its atmosphere is different from that of the earth.
单项选择题
A．Why species don’t avoid extinction by adapting.B．Why species become extinct at the rate they do.C．Why humans aren’t extinct.D．How many species aren’t extinct.
A．Why species don’t avoid extinction by adapting.
B．Why species become extinct at the rate they do.
C．Why humans aren’t extinct.
D．How many species aren’t extinct.
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