A：pollution, pollute
B：polluted, pollution
C：pollution, pollution
D：pollute, polluted
The Children were so excited that they could speak.
①相等的角是对顶角；
②如果三角形中有一个角是钝角，那么另外两个角为锐角；
③若两直线平行，则内错角相等；
④若x＞0，则|x|=x．
其中是真命题的有几个（ ）
