填空题

At the first sight the planet Mars does not appear very welcoming to 62. ______.
any kind of life. It has very little oxygen and water, the temperature at
night is below -50 degrees and winds of 100 miles per hour cause severe
dusty storms. However, the surface of the planet seems to show that 63. ______.
water flowed across at some time in the past, and it is believed that there 64. ______.
is enough ice at the poles to cover the planet with water if il melts. 65. ______.
Although there is no life on Mars. some scientists think that there may
have some form of life a long time ago. At that time, the planet had active 66. ______.
volcanoes; the atmosphere was thinner and warmer; and there was water. 67. ______.
In fact, in some ways Mars may have been different to earth, where life 68. ______.
exists.
Some people believe that Mars could support life in the future if the
right conditions were produced. The first step would be to warm the
planet used certain gases which trap the sun’s heat in the planet’s 69. ______.
atmosphere. By warmth, water and carbon dioxide, simple plants could 70. ______.
begin to grow, These plants could slowly make Mars habitable. It is　　　　　　　　　
established that the whole process might spend between 100,000 and 200,000 71. ______.
years. In the meantime, people could begin to live on the planet in special
closed environments. They would provide a lot of useful information about
conditions on Mars and the problems connected with living there.