单项选择题

What leads to the formation of a black hole

A．The structure of a star.
B．A collision between two stars.
C．The attraction of two large stars.
D．The shrinking of a large star by its own gravitational force.

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热门试题

单项选择题

Why does the author put neutron star in quotation marks

A．It is a special term of astronomy.
B．It is an invented term.
C．He is quoting an authority.
D．He is using the term ironically.

单项选择题

According to Einstein's theory, objects in the area of a black hole

A．are gathered in its center.
B．strike against one another frequently.
C．do not have absolute space.
D．are relatively brighter.