工业和生活污水是环境污染的重要来源，污水处理是环境保护的重要措施，氧化塘法就是一种利用自然生态系统净化污水的方法。氧化塘是一个大而浅(水深约2m)的池塘，下图表示其生物群落和非生物环境。试分析回答问题：

根据拼音写出相应的词语。

如图，P是AB所对弦AB上一动点，过点P作PM⊥AB交AB于点M，连接MB，过点P作PN⊥MB于点N．已知AB=6cm，设A、P两点间的距离为xcm，P、N两点间的距离为ycm．（当点P与点A或点B重合时，y的值为0）

小东根据学习函数的经验，对函数y随自变量x的变化而变化的规律进行了探究．

下面是小东的探究过程，请补充完整：

    I had worked that day, as a nurse. Now I faced the dirty supper dishes. I wanted to 1why Jimmy hadn't phoned as usual to say “Good night”to Bob and Tom. “Maybe Daddy's 2 working on an accident,” I said to Bob. “Go to3 now. You'll see him in the morning.”Soon there was a knock at the door. “There4 be something wrong with your phone,” my neighbor told me. “The City Police Station wants you to 5.”
    I went into the living room and dialed. Then I 6 the words every police wife fears (害怕): “Your husband has been hurt.” When I reached the hospital, my heart sank (下沉). The entrance was jammed with TV-news trucks. In the 7  I saw Jimmy’s best friend, Smith. “Just tell me -is he alive ?” I asked.
    Smith 8. and didn't answer. Then I found my younger sister, Mandy. “He’9s ”she told me, and we began to cry together.
Later, Smith told me 10 had happened.
    In the morning, when my little Bob asked, “Where's Daddy?” I 11  him into my arms and tried to explain. “A bad man 12 Daddy last night.” I said. “Daddy can't come home any more. He's in heaven(天堂) now.”
My son looked at me, his blue eyes 13 the picture of trust(相信). “Do they have14 in heaven ?”he asked. “Can I call him ?”
“No, Bob, Daddy still loves you, but Daddy can't15”.

在装满水的玻璃杯内，可以不断地轻轻投放一定数量的大头针，水也不会流出，这是由于（ ）