将一些相同的“○”按如图所示的规律依次摆放，观察每个“稻草人”中的“○”的个数，则第20个“稻草人”中有____个“○”．

如图所示，OB是一束光线由空气射到水面后的反射光线，在图中画出入射光线，并画出折射光线的大致方向．

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复数z= $\frac{2i}{1+i}$ 的共轭复数是（   ）

若厄尔尼诺现象发生，则不可能出现（   ）

选词填空阅读下面短文，从方框中选择单词，根据实际情况用其适当形式填空，使短文意思完整、通顺。每空一词，每词只能用一次。

 A man was tired of living in his small house in the country.  He wanted to sell it and buy a ____  one than the old one nearby. He tried to sell it for a long time, but____ wanted to buy it. So at last, he decided to use a house salesman. The salesman soon put a picture of the man's house on a magazine. ____  days later, the owner saw a very beautiful picture of the house, with a wonderful introduction to its gardens, on a magazine. After the house owner had read ____ the whole introduction, he at once called up the salesman and said,“I'm sorry, but I've decided not to sell this house after all. After ____  your introduction, now I know that It's just the kind of house I'm going to live in for the rest of my life.