Some scientists believe that Mars is the planet with the highest chance of supporting human life away from Earth.

They believe that it’s possible for human to reach Mars by 2030. However, there are many things to prepare before this can happen. 【小题1】 Recently, scientists have sent robots to Mars to gather information about the planet.

Putting people on Mars will include (包括) planning how a person will live on Mars. At its shortest distance, Mars is 55 million kilometers away from Earth. 【小题2】 And astronauts would have to stay on Mars for over 18 months before Earth and Mars are at their closest distance again. The difficulties would include how much food and other things would be needed for over two years in space and how such things would be carried.

【小题3】 They would need to prepare both their minds and bodies for such a long trip away from Earth. NASA set up a special research building in Hawaii. A group of astronauts stayed in this research building for 366 days. During their stay, they had to deal with what they might have to deal with on Mars. 【小题4】 They had to live with each other in a very small space. They also had to deal with the problems of having lots of time with little or nothing to do. They couldn’t receive help from people outside for the whole time they were inside.

【小题5】 There is no doubt about it.

根据材料内容，从下面五个选项中选出能填入文中空缺处的最佳选项，使短文意思通顺，内容完整。

A．Astronauts have been the key to the plan.

B．For example, they had to be fed with bad food.

C．One day humans will be able to live on Mars.

D．Scientists must make some research on Mars well.

E．So it would take about 6 months for a one-way trip.