Millions of stars are travelling about in space. A few form groups which travel together, but most of them travel alone.
And they travel through a universe which is so large that one star seldom comes near to another. For the most important part each star makes its journey in complete loneliness, like a ship on an empty ocean. The ship will be well over a million miles from its nearest neighbour. From this it is easy to understand why a star seldom finds another anywhere near it.
We believe, however, that some two thousand million years ago, another star wandering(漫游) through space, happened to come near our sun just as the sun and the moon raised its tides(潮汐) on the earth, so this star must have raised tides on the surface of the sun. But they were very different from the small tides that are raised in our oceans; A large tidal(潮汐的) wave must have travelled over the surface of the sun, at last forming a mountain so high that we cannot imagine it. As the cause of the disturbance came nearer, so the mountain rose higher and higher. And before the star began to move away again, its tidal pull had become so powerful that this mountain was torn to pieces and thrown off small parts of itself into space.
These small pieces have been going round the sun ever since. They are the planets.
Most stars are _________________________.

A．following a regular path in space

B．moving about without a fixed course

C．seldom wandering about in the universe

D．always travelling together

Some two thousand years ago, the mountain on the sun was raised probably because _____________.

A．the star moved away from the sun

B．another star happened to come near the sun

C．the sun and the moon raised the tides on the earth

D．a large tidal of wave travelled over the surface of the sun

The article suggests that _______________.

A．how space formed

B．our earth exists before the sun

C．no one knows where the earth comes from

D．our earth used to be a high mountain in the sun

The expression “the cause of the disturbance” refers to ________.

A．the large tidal wave	B．the powerful tidal pull
C．the star coming near the sun	D．one of sun’s planets

In the article, the writer mainly wants to tell us ______________.

A．where the planets in the universe came from

B．how the high mountains were formed on the sun

C．that the universe is so large that we cannot imagine it

D．why the tides over the surface of the sun were so powerful