[单项选择]The gravitational attractive of a black hole is extremely intense, but it would be no stronger ___ of a normal star of the same mass.
A. than that
B. as is
C. than it is
D. from which

[单项选择]The gravitational pull of the earth and moon is important to us as we attempt to conquer more and more of outer space. Here’s why.
As a rocket leaves the earth, the pull of the earth on it becomes less and less as the rocket roars out into space. If you imagine a line between the earth and the moon, there’s a point somewhere along that line, nearer to the moon than to the earth, at which the gravitational pull of both the earth and the moon on an object is just about equal. An object placed on the moon side of that point would be drawn to the moon. An object placed on the earth side of that point would be drawn to the earth. Therefore, a rocket need be sent only to this "point of no return" in order to get it to the moon. The moon’s gravity will pull it the rest of the way.
The return trip of the rocket to the earth is, in some ways, less of a problem. The earth’s gravitational field reaches far closer to the moon than does the moon’s to earth. Thus, it will be necessary to f
A. the rocket
B. the pull of the earth
C. the pull of the moon
D. the gravitational pull of the earth and moon

[填空题]black powder

[单项选择]　Black Holes 　　Most scientists agree that black holes exist but are nearly impossible to locate.A black hole in the universe is not a solid object,like a planet,but it is shaped like a sphere (球体).Astronomers(天文学家)think that at the center of a black hole there is a single point in space with infinite(无限的)density(稠密).This single point is called a singularity (奇点).If the singularity theory is correct,it means that when a massive star collapses,all the material in it disappears into the singularity.The center of a black hole would not really be a hole at all,but an infinitely dense point.Anything that crosses the black hole is pulled in by its great gravity. 　　Although black holes do exist,they are difficult to observe.These are the reasons. 　　● No light or anything else comes out of black holes.As a result,they are invisible to a telescope. 　　● In astronomical terms,black holes are truly.For example,a black hole formed by the collapse of a giant star would have an event horizon(视
A. Right
B. Wrong
C. Not mentioned