某陆地生态系统中，除分解者外，有甲、乙、丙、丁、戊5个种群．调查得知，该生态系统中的各种群已经形成了较为稳定的食物关系，食物网中下一级生物只能获得上一级生物大约10%～20%的能量．一年内输入各种群的能量数值如下表所示，表中能量数值的单位相同．

问答下列问题：

    Hello! I'm Petty. This is my day. It's six forty. It's time to get up. It's seven o'clock. It's time to go to school. It's eleven thirty. It's time for lunch. It's four twenty. It's time to go home. It's eight thirty. It's time to go to bed.

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A.    B. C. D.   E.

油菜素甾醇对维持顶端优势，促进种子萌发及果实发育有重要作用．据此推测最合理的是（　　）

A、B两球的质量均为m，两球之间用轻弹簧相连，放在光滑的水平地面上，A球左侧靠墙．用力F向左推B球将弹簧压缩，如图所示．然后突然将力F撤去，在撤去力F的瞬间，A、B两球的加速度分别为（   ）