如图，在针孔成像问题中，根据图形尺寸可知像 的长是物AB长的（    ）

如图是一额定功率为1000W电饭煲及其能效标识，已知电热效率80%，保温能耗40W•h（保温1h消耗的电能）．家庭电路电压220V，某一次煮饭，电饭煲放一定质量的米，加适当比例的水，混合后总质量1000g混合物比热容近似看作4.0×10³J/（kg．℃），煮熟后的米饭大约800g．米和水初温20℃，加热到100℃开始沸腾．（水沸腾前，混合物质量近似认为不变，100℃时1g水汽化需吸热大约2400J）．

阅读短文，下列问题
A
    One night there was a heavy snowstorm(暴风雪), and in the morning Mr. Smith's garden was full of snow. Mr. Smith wanted to take his car out, so he asked a man to clean the road from his garage to his gate, he said to the man,"Don't throw any snow on that side, because it will damage (破坏) the shrubs in my garden and don't throw any on the other side, because it will break my fence; and don't throw any into the street, or the police will not be pleased. "Then Mr. Smith went out.
    When he came back, the road was clean and there was no snow on the shrubs, or the street. Mr. Smith was pleased until he opened the garage to get his car out. There was full of snow from the road, and his car was somewhere under it all. 

历史小论坛：“打倒列强！打倒列强！除军阀，除军阀，国民革命成功，国民革命成功！齐欢唱，齐欢唱！”奇奇正起劲地唱着“国民革命军军歌”，明明打断了他，说道：“唱的倒是不错，那你知道国民革命运动的结果如何？”“国民革命运动取得了重大成果，但最后还是失败了。”明明说：“不错，那你告诉我，国民革命运动最大的功绩是什么吗？失败的原因又是什么？”奇奇回答了一部分，明明说他答得不太全面，请你给个比较全面的答案吧。

已知f（x）=2^x﹣2^﹣x，a=（ $\frac{7}{9}$ ） ${}^{\frac{1}{2}}$ ，b=（ $\frac{9}{7}$ ） ${}^{\frac{1}{2}}$ ，c=log₂ $\frac{7}{9}$ ，则f（a），f（b），f（c）的大小顺序为（   ）