A black hole is a spot in space that has     1     (power) gravity. Its gravity is so strong that it pulls everything nearby into it, stars, planets and other things. Black holes form when a star dies. When that happens, a huge amount of matter crowds into a very small space, which     2    (become) very dense. Black holes     3     (talk) about in 1783 first. That year, one scientist said that in the universe, there might be places with strong gravity to trap light, although he didn’t use the term “black hole”.

World leaders are planning to return to the moon in the near future. Two companies have also made a decision     1     (support) space travel. They will give 30 million dollars to the first members who send a vehicle to the moon and send video back to Earth over the Internet. In addition to     2     (make) a lot of money, the winners will also make history. In the 1400s, Spanish leaders     3     (give) Columbus money to explore the world; in return, they learned about a whole new part of the world. Today’s lunar explorers are similar. Who knows     4     they will discover?

Since she was three years old, Elsa has focused on becoming an astronaut. She was watching childhood favorite cartoon The Backyardigans,    1     five friends go on adventures right in their own background. During one such episode (集)，the Backyardigans go on a mission into space. After watching the episode, Elsa     2    ( attract) and began asking her dad questions about space. However, not     3    (know) much about this， Elsa's dad together with her searched for     4     they can do to help fuel Elsa's dream. Now at seventeen years old, she is already widely predicted to become one of the first people to go to Mars in a few decades.

The earth, the planet on     1     we are living, is the third planet from the sun. It came from the shrinking (收缩) of a vast cloud of dust and gas in outer space. Many scientist believe that the earth,   as well as the sun and the other planets in our solar system,     2     (form)   at least five billion years ago.   The earth is slightly flattened at the North and South Poles,     3     it would look like a perfect ball if you were far out in space.

No one knows exactly     1     the earth began. However, according to a widely accepted theory, the universe began     2     a “Big Bang”. Then the dust     3    (settle) into a solid globe. As the earth cooled down, water began to appear on its surface. Many     4    (science) believe that it was the presence of water that allowed the earth to dissolve     5    (harm) gases and acids into oceans and seas, which made it possible for life to develop.

Millions of years later, the first small plants appeared on the surface of the water. Their development     6    (follow) by early shellfish, all sorts of fish, green plants and land animals. Reptiles     7    (produce) young generally by laying eggs while mammals gave birth to young baby animals. Dinosaurs existed on the earth for over 140 million years before they suddenly disappeared. The reason     8     they disappeared still remains a mystery.

Finally, humans appeared and spread all over the earth. But they are putting too much carbon dioxide into the atmosphere, which prevents heat from     9    (escape) from the earth into space. As a result of this, people believe the earth may become too hot to live on. So     10     life will continue on the earth will depend on how this problem can be solved.

6 . Astronauts are people who go out into space. Being an astronaut is an exciting job. While in space, astronauts can look down and see     1    （cloud）, land, and water. They can even see the moon up close. Astronauts get the chance     2    (see) more stars than you or I have ever seen. Being an astronaut may be exciting,     3     it is not an easy job. A person who     4    (want) to be an astronaut has to study for years. There are many things an astronaut must learn to do before going into space.