Theearthistheonlyplanetthatscientistsarecertainhaslife....

問題詳情：

The earth is the only planet that scientists are certain has life. What does the earth have that other planets in our solar system don't have? For one thing, the earth is just the right temperature. As 61. ________ third planet from the sun, the earth seems to be just the right distance away. The planets that are closer to the sun are 62. ________ (extreme) hot and their surfaces are baking in the sun. The farthest planets are frozen balls.

When the earth developed, it 63. ________ (cover) by many gases. The gases caused the earth 64. ________ (be) hot. But something 65. ________ (amaze) happened. The temperature was just right for thick clouds to form. It rained very hard for a long time. This gave the earth its oceans. Water made 66. ________ possible for plants to grow. Then the plants created oxygen in the atmosphere, 67. ________ is the gas that humans and animals breathe.

Mars is the only planet in the solar system that seems to be anything like the earth. It is 68. ________ (small) than the earth and it is quite a bit cooler. But it is not too cold for humans. The most unexpected sight on Mars is dried-up river beds. However, it is believed 69. ________ Mars was once much wetter. Does this mean there could have been living things on Mars? Scientists are not sure, but there 70. ________ (be) no sign so far.

【回答】

61. the               62. extremely           63. was covered               

      64. to be             65. amazing            66. it        

      h            68. smaller          69. that                

      70. has been

知識點：語法填空

題型：未分類