Humans may live on another planet one day! That 【小题1】 (seem) impossible years ago. But now the idea may come true. According to Stephen Hawking, a British 【小题2】 (science), humans only have about 1,000 years to live on the earth. It means that humans 【小题3】 (fly) to another planet in 1,000 years. In fact, we have found one red planet Mars (火星). Experts have found that there 【小题4】 (be) water on it. The idea of living there looks possible. Thanks to science, the steps to Mars are getting 【小题5】 (fast) than before. For example, in 2013, Dutch experts 【小题6】 (plan) the first plan to put humans on Mars. They offered people one-way tickets to go and build a new home on Mars. 【小题7】 it was dangerous, over 200,000 people still wanted to take part in it. 【小题8】 the evening of September 21, US experts showed another plan to get humans to Mars in six years. They are also doing many 【小题9】 (prepare) to help people get back to the earth. I’m looking forward to 【小题10】 (live) on Mars. Will you join us?

Earth — our home and our planet, is a truly amazing place to live. Think about so many kinds of lives living on Earth. If you have ever flown on a plane, you’ve 【小题1】 (get) a new respect（尊重） for Earth.

Earth is the only planet known to support life. The 【小题2】 (difference) in life forms on Earth are far more than our imagination. On the one hand, there are tiny microbes（微生物）and they can only 【小题3】 (see) through a microscope. On the other hand, there are 30-metre long whales that swim through our oceans, covering 【小题4】 (thousand) of miles in their ravels.

We have mountains 【小题5】 （near）ten kilometres high and valleys（峡谷）many kilometres deep. The 【小题6】 (deep) valleys of all are underwater. These undersea valleys can reach 11 kilometres in depth. And yet, even under the pressure of the water at that depth, life still exists. Look at the trees around you. Some trees are over 100 metres tall. That looks 【小题7】 a 30-storey building! And they can be 1,000 years old. We have soft grass 【小题8】 (walk) on, and trees with needles（针叶）so sharp that they can make your finger bleed if you touch them.

But the most amazing thing about this planet is the people. There are more than seven billion people 【小题9】 (live) on this planet. We live in different places and speak different languages, 【小题10】 we live on the same planet and enjoy the same sun, the same air and the same water.

Earth — our only home, our great planet. Humans really are so lucky to have such a wonderful place to call home.

According to our guidebook,Uranus(天王星)was the first 【小题1】 to be discovered with a telescope.It is 2,871 【小题2】 kilometres from the sun.This is twice as 【小题3】 as the planet Saturn(土星)is from the sun.Uranus is four times the 【小题4】 of the earth,but smaller than Saturn,and it is so far away 【小题5】 we can't see what it looks like.Only 【小题6】 spacecraft has been to Uranus.It was Voyager 2,in 1986.As Voyager 2 【小题7】 close to Uranus,the world saw the 【小题8】 picture of this faraway planet.The world saw a blue planet made of gas.

Summer on Uranus lasts for 42 years.During this time it is 【小题9】 on the other side of the planet.The sun shines on each side for 42 years at a 【小题10】 as it goes around the sun.