调压变压器就是一种自耦变压器，它的构造如图乙所示．线圈AB绕在一个圆环形的铁芯上，CD之间输入交变电压，转动滑动触头P就可以调节输出电压．图乙中两电表均为理想交流电表，R₁、R₂为定值电阻，R₃为滑动变阻器．现在CD两端输入图甲所示正弦式交流电，变压器视为理想变压器，那么（   ）

    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.