单项选择题

When a large star explodes, the gravity compacts every piece into（）

A. the creation of new entities
B. an explosion of huge stars
C. the tiniest particle
D. the same amount of mass
E. the existence of black holes
F. a fraction of an inch

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热门试题

单项选择题

Researchers find it difficult to make algae produce hydrogen efficiently because（）

A．removing the sulfate slows down the hydrogen production.
B．It is hard to create an airfree environment.
C．It is expensive to remove the sulfate from the environment.
D．the algae’s cells work slowly if there is no oxygen in the air.

单项选择题

There is a mounting pressure on public lands to satisfy US energy demands because（）

A．the US is demanding more and more energy.
B．many Americans are unhappy with energy development in foreign countries.
C．quite a few public lands are banned for energy development.
D．many Americans think public lands are being abused.