The clock struck(敲) eleven at night. The whole house was quiet. Everyone was in bed except me. Under the strong light, I looked sadly at a huge pile（堆） of those trouble things —books.
   I was going to have my exam the next day. “When can I go to bed?” I asked myself. I didn't answer. And I could not. The clock struck twelve. “Oh, dear! Ten more books to read before I go to bed!” We students are the most wretched ones in the world. Dad does not agree with me on this. He did not have to work so hard when he was a boy.
   The clock struck one. I was quite hopeless now. I forgot all I did learn. I was too tired to go on. I did the only thing I could. I prayed（祈祷）, “My god, please let me pass the exam tomorrow. I will work hard next time, Amen.” My eyes were so heavy that I could hardly open them. A few minutes later, with my head on the books, I fell asleep.

在△ABC中，AB=AC，∠A=60°，点D是线段BC的中点，∠EDF=120°，DE与线段AB相交于点E，DF与线段AC（或AC的延长线）相交于点F．

科学家对某湖泊进行了生态系统营养级和能量流动的调查。表中的①-④分别表示不同的营养级，⑤为分解者，表中单位是J/cm² a(焦每平方厘米年)，NP（生物体贮存的能量）=GP（生物同化作用所固定的能量）—R（生物呼吸消耗的能量）。下列叙述中正确的是（    ）