粮食价格主要由什么形成的？

阅读理解。

     Sally was a student. It was going to be her mother's birthday. She wanted to buy her a present that would

be nice and useful but not expensive.

     She went shopping after a quick and simple lunch. After she looked for half an hour, she found a shop that

was selling cheap umbrellas, and she decided to take a black one.

     She thought, "Mom can carry it when she is wearing clothes of any color." So she bought a lovely black

umbrella and took it to school with her until her class finished.

     On her way home on the train she felt hungry because she had so little for lunch. So she went to the buffet

car (餐车). She left the umbrella on her seat. But when she got back, it had gone!

     Sally began to cry. The other passengers felt very sorry for her and asked what the matter was. She told

them the black umbrella she bought for her mother had gone, and she had to get off at the next station. After

the three passengers heard this, they asked her for her mother's address so that they could send the umbrella

to her if someone took it by mistake and brought it back.

     And now a week passed. Sally got a letter from her mother. It said "Thank you very much for your lovely

gifts, but why do you send me three black umbrellas?"

1. Which sentence has the same meaning as "Mom can carry it when she is wearing clothes of any color"?

A. Mom must carry it when she is wearing any clothes.

B. Mom is beautiful in any clothes.

C. The color of the umbrella is OK for Mom's clothes of any color.

D. Mom can buy any clothes that she likes to wear.

2. Where did Sally find the umbrella missing?

A. On the train.

B. At her school.

C. At the train station.

D. In the shop.

3. From the passage, we can know that _____.

A. Sally's mother would write to her if she didn't receive the gift

B. one of the umbrellas must be sent by Sally

C. the three umbrellas were sent by the three passengers

D. nobody on the train took away the umbrella

4. The best title for the story is "_____".

A. A lucky girl

B. The story of an umbrella

C. On the train

D. A happy mother

5. The writer wants to tell us _____.

A. we should look after our things when we are traveling

B. if we show our love to others, we can get love from others

C. we should often send our parents gifts

D. it's no use crying when we are in trouble

（14分）（2011•广东）设a＞0，讨论函数f（x）=lnx+a（1﹣a）x²﹣2（1﹣a）x的单调性．

高压配电系统中性点接地方式有（）

A、中性点直接接地

B、中性点不接地

C、中性点经消弧线圈接地

D、中性点经低电阻接地

中共十五大报告指出：“一个世纪以来，中国人民在前进道路上经历了三次历史性的巨大变化。”这三次历史性变化是（）

①辛亥革命推翻了君主专制制度②中华人民共和国的成立和社会主义制度的建立

③香港回归，洗雪了中 * * 百年耻辱④改革开放，为实现社会主义现代化而奋斗

A、①②③

B、①②④

C、①③④

D、②③④

清理过滤器时，应先打开过滤器的排污阀，然后打开过滤器上的（）。

A.挡板阀

B.针形阀

C.引压阀

D.放气阀