岳飞受到人们尊敬的根本原因是（     ）

① 先把绿色植物在暗处放置24小时，目的是____ 。

② 实验时要用黑纸片把叶片的一部分遮盖起来，目的是____ 。

③ 在阳光下照射30分钟后，将摘下的叶片取下黑纸，放入酒精中隔水加热，该步骤的目的是____ 。

④ 给处理过的叶片滴加碘后，叶片的见光部分呈____ 色，遮光部分____ 色。

(C)

    If someone asks you, "What colour is the sky?" I think the answer will be "blue". I'm afraid that you are wrong. Because the sky has no colour.

    What's in the sky? Is the sky full of air? I'm sure that you have asked these questions. We all know that there's air all around the world. We can not live without air. Planes can't fly very high because as they go higher, the air gets thinner. If we go far enough away from the earth, we can find that there is no air. The sky is space（太空）. In this space there is nothing but the sun, the moon and the stars.

    People always want to know more about other worlds in space. They have looked at them through （通过） telescopes （望远镜） and in this way they have known much. They know a lot about the moon now. But they want to know more about space. I'm sure they will go farther and farther until they know all about it.