列车奔驰要受轨道的约束，飞机飞行要受航线的约束，大河奔流要受河岩的约束，体育规则的约束，人类生产、生活无时无刻不受到自然的、社会的、自身的方方面面的约束……这说明（  ）

阅读理解

     Hello! My name is John, I have a happy family. There are four people in my family. They're my father, my mother, my baby sister and I. We have a beautiful garden. There are two trees and some flowers in it. There are some apples on the tree. Do you like apples and flowers? Welcome to my home.

    I can't help but feel ____(concern) about the ____(destroy) of tropical forests. It is one of the most serious environment problems today. From ____ I know, people are damaging thousands of square ____(kilometer) of forests every day. This is killing hundreds of wild animals that live in the forests.

    ____(fortunate), we do nothing but talk about it. We don't do anything ____(protect) the forests. We need to stop people doing it. There should be ____(strong) laws. I think that people who cut ____ forests should go to prison. That's what should happen to people who destroy the forests and kill wildlife.

    In my opinion, we, human beings, must protect wildlife ____ future generations. Hopefully, our children ____(be) more responsible than we are today.

先填出成语中所缺的字，然后解释。

____不相识   莫____ 其妙   痛心____ 首

无____于事   别____ 匠心   错____ 复杂

求证:△ACE是等边三角形.