The dense black cumulonimbus clouds surrounding the eye of a hurricane are called ______．A

A.正确

B.错误

A.Y.是

B.N.否

A.Y.是

B.N.否

A.正确

B.错误

A) dark

B) dense

C) black

D) bold

What is a black hole？ Well, it is difficult to answer the question,

as the terms we would normally use to describe a scientific phenomenon __1__are adequate here. Astronomers and scientists think that a black hole is __2__a region of space which matter has fallen and from which nothing can __3__

escape—not even light. But we can’t see a black hole. A black hole __4__exerts a strong gravitational pull and yet it has no matter. It is only space—or thus we think. How can this happen？ __5__

The theory is that some stars explode when their density increases to a particular point; they “collapse” and sometimes a supernova occurs.

The collapse of a star may produce a “White Dwarf” of a “neutronstar”—

a star which matter is so dense that if continually shrinks by the force of __6___its own gravity. But if the star is very large, this process of shrinking may be so intense that a black hole results in. Imagine the earth reduced to the __7__size of a marble, but still having the same masses and a stronger __8__gravitational pull, and you have some ideas of the force of a black hole. __9__And no matter near the black hole is sucked in. __10__

A.decrease

B.merit

C.dense

D.isadvantage

A. PIM sparse - dense mode and PIM dense mode require an RP on the network.

B. PIM sparse mode and PIM dense mode require an RP on the network.

C. PIM sparse mode interfaces are always added to the multicast routing table in a router.

D. PIM sparse mode and PIM sparse - dense mode require an RP on the network.

E. PIM dense mode interfaces are always added to the multicast routing table in a router.

F. PIM sparse - dense mode acts as PIM dense mode if an RP is not known.