函数的三要素：____，____，____．相同函数的判断方法：①____；②____（两点必须同时具备）

执行如图所示的程序框图，若输入如下四个函数：①$f\left(x\right)=\sin x$；②$f\left(x\right)=\cos x$；③$f\left(x\right)=\frac{1}{x}$；④$f\left(x\right)=x^2$，则输出的函数是（     ）

— Yes. But now I'm used to __________ in the swimming pool.

-- Is it           to protect the earth against heavy pollution?

-- No, I don't think so. If everybody takes actions now, it will become better.

forest的复数形式是____.