4．
阅读理解
Our nearest
neighbour is the moon. In the sky, the moon and the sun seem to be of the same
size because the moon is much nearer.
The moon makes the
tides（潮汐）—the changes in
the level of the sea. The moon and the sun together pull the sea. In some parts
of the world, the difference between "high tide" (when the sea is
very near to the land) and "low tide" (when the sea is far away from
the land) is very big. This is very important to ships.
The moon is very
different from the earth. Gravity（地心引力）on the moon is one-sixth of that on the earth. There isn't any air.
During the day, the part of it that face the sun is very, very hot but at night
it is very, very cold. Nothing can live on the moon.
If the moon goes
between the earth and the sun, we have an eclipse of the sun（日食）. The moon stops
the light from the sun and it is dark in the day.
If the earth goes
between the moon and the sun, we have an eclipse of the moon. The moon goes
into the shadow（影子）of the earth and it disappears for a few minutes.
