左边给定的是纸盒的外表面，下面哪一项能由它折叠而成（）

A:A B:B C:C D:D

[范文]
The two pictures seem rather similar at first glance, but they are totally different. The first picture is of a peasant boy, carrying a heavy bundle of rice straw. His hope might be to have a school to attend. In the second picture, a student almost gets buried under a heavy bag of books. What he wishes maybe that he should no longer attend school What results in this big difference between the two boys’ ideas about attending school
These two pictures are to indicate some problems in the present education system in China. In the poor countryside, especially in some western parts of China, the- education is so poor, even without any buildings for classrooms, let alone competent teachers. Children there are sometimes forced to leave school because of poverty. However, the situation is totally different in the cities. Almost all the children in the cities can have regular education. They can enjoy the bright classrooms and adequate facilities. But they have their own problems. They are so overburdened with endless homework that they even want to quit their studies.
Given the problems above, our government has taken some measures. "The Hope Project" has been in operation to ensure that children in the poor areas can gain access to education. Some strategies have also been put into force to reduce the pressure on the students. However, there is a long way to go in the improvement of our overall education conditions. People of all walks should feel obliged to make some contributions to our education.

这个标志的含义是提醒车辆驾驶人前方是过水路面或漫水桥路段。

解：[e521cb416bc2ca2a.png]，

①-②得：y=2，

将y=2，代入①，得x=14，

则方程组的解为[6f31887298c188d4.png]．

A:2 B:﹣2 C: D:﹣

在□ABCD中，点E.、F.在AC上，且∠ABE=∠CDF，

求证：BE=DF.

（第19题）

证明：因为四边形ABCD是平行四边形

所以AB∥CD，AB=CD，因为AB∥CD，所以∠BAE=∠DCF

所以在△ABE和△CDF中，所以△ABE≌△CDF，所以BE=DF.

已知是正整数，则正整数a＝____________.

抛物线的顶点坐标是（ ）

A:（2，0） B:（-2，0） C:（1，-3） D:（0，-4）