如图，在底面为矩形的四棱锥 $E-ABCD$ 中， $DE\perp$ 平面 $ABCD$ ， $F$ ， $G$ 分别为棱 $DE$ ， $AB$ 上一点，已知 $CD=DE=3$ ， $BC=4$ ， $DF=1$ ，且 $FG\parallel$ 平面 $BCE$ ，四面体 $ADFG$ 的每个顶点都在球 $O$ 的表面上，则球 $O$ 的表面积为（    ）

       Taking away a city's rubbish is a big job. Every day trucks come into a city to collect it. Most rubbish is made up of things we can't eat or use. If we kept these things we would soon have a mountain of rubbish.
       In some cities the rubbish is collected and taken outside of the city to a dump(垃圾站). Often the city dump is placed where the ground is low or there is a big hole. The kitchen rubbish is broken into small pieces and sent into the sewage system. The sewage system takes away the used water from toilets, bathtubs(澡盆) and other places.
        To keep mice and flies away, some earth is used to cover the newly dumped rubbish. Later, grass may be planted on the rubbish-filled land. Finally, a house or a school may be built there, and then you’d never know that this had once been an old rubbish dump.
       In other cities the rubbish is burnt in special places. The fire burns everything but the metal. Sometimes the metal can be used again in factories where things are made of metal. The food parts of rubbish are put in special piles where they slowly change into something called humus(腐殖土), which looks like black earth. It is rich with kinds of things that feed plants and help make them grow.

以下是有关SO₂、Cl₂的性质实验．

神经系统由____、脊髓和它们发出的神经组成，神经调节的基本方式是反射，“谈虎色变”这类与语言文字有关的反射是最复杂的，也是____的。

Please make a note ______ you have any questions when reading.