It is dangerous for little children to swim in the river.为什么这里用to swim
问题描述：
It is dangerous for little children to swim in the river.为什么这里用to swim
答
固定句型
It's + 形容词 + for sb.+ to do sth.
真正的主语是动词不定式 to do sth.
To swim in the river is dangerous for little children.有点头重脚轻,所以用形式主语it