一个池塘中含有生产者（浮游植物）、初级消费者（植食性鱼类）、次级消费者（肉食性鱼类）、分解者（微生物）。其中生产者固定的全部能量为a，流入初级消费者、次级消费者、分解者的能量依次为b、c、d，下列表述正确的是（）
A.a=b+d
B.a>b+d
C.a
参考答案：B
解析：
生态系统中的能量流动从生产者固定太阳能开始。能量流动特点为单向，逐级递减。生态系统中，能量流动只能从第一营养级流向第二营养级，再依次流向后面的各个营养级，因此是单向不可逆转的。所以初级消费者、次级消费者、分解者的能量加起来都小于生产者固定的全部能量，故选B。
考点：生态系统的功能
点评：本题难度一般，要求学生识记生态系统的功能的相关知识，考查学生对能量流动的理解。
It is interesting to know what people of different nations like to be best. In France, when a woman enters a café or restaurant, she is freely discussed, not only about her appearance but about her past and future as well. She invites looks in the street whether she is beautiful or plain. There is no better way for a woman to get back her self-confidence than a walk in the streets of Paris or Marseilles, and woman really like that. In Italy, people love talking. They sit about in cafes, exchanging news and discussing politics. They do not hesitate to ask questions about the family, income and private life of anybody who happens to be there. The Swiss eat as a pastime. Ladies walk into a teashop, eat a couple of ice creams and a large piece of chocolate cake, and then leave, complaining about their weight.] For the Americans, the greatest fondness is said to be the push of buttons. You push a button in the lift, you push a button for cigarette, chewing gums, stamps, even for a life insurance. You can even push a button to get married and another button to get divorced. In England, waiting in a line is national passion. The English will form a line whether they have the opportunity or not. Long queues can be seen, for example, at stations when the train is practically empty and everybody can have a seat.
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