A

Some of the world's most important scientists think the idea of people living on Mars will come true one day. Stephen Hawking believed humans must move into space to survive. “Once we spread out into space and establish independent colonies, our future should be safe,” he said.

However, scientists will need to terraform Mars for people to be able to live. One of the main goals of terraforming Mars is to warm it up because the average temperature there is about -60 One idea for wanning Mars is to build factories there that produce greenhouse gases. This could take many centuries. However, it should lead to rainfall and the growth of plants, resulting in more air that people can breathe.

Another big concern for scientists is whether humans can move to Mars and still stay healthy in mind and body. As a test, six people lived in a Mars-like environment in Hawaii for a year before “returning to Earth” recently. It was a 1,200-square-foot room that was on the side of a volcano and used the sun for energy. Christiane Heinicke, one of the people who lived there, said that one of the biggest issues was feeling bored. So humans on Mars would always need to keep themselves busy with various activities. Another important finding was that the people living together should all be able to get along and work together.

One particular organization based in Europe is planning to send the first humans to Mars before 2030. The organization believes that its project is giving people worldwide the chance to be part of the first human crew ever to live on Mars for good. However, many experts think the project’s cost of US$6 billion is too low for it to be successful. The American space agency NASA believes that sending people to Mars would cost about US $100 billion, although this estimate is based on bringing them back to Earth, too. Regardless, it seems that humans living on Mars may well happen a lot sooner than most people believe.

21. What's Stephen Hawking’s opinion about settling on Mars?

A.  It makes sense to live on Mars.

B.  There is no need to spread out into space.

C.  Moving into space is a dream impossible to fulfill.

D.  Our future will not be secure unless independent kingdoms are built.

22. What does the underlined word ‘'terraform” in Paragraph 2 refer to?

A.  Warm up Mars.

B.  Make Mars more like Garth.

C.  Build more factories on Mars.

D.  Accelerate the growth of plants on Mars.

23. What does the author think about nr«*iving to Mars?

A.  Living on Mars is bori but good.

B.  It is too costly to send humans to Mars.

C.  Humans' health will be greatly affected.

D.  Moving to Mars is expected in the near future.

24. Which can be the best title of the passage?

A. Safe on Mars?     B. Boring on Mars?

C. Homes on Mars?    D. Challenges on Mars?