在罗塞塔3级1单元1课有这么几个句子,如下:The two girls are talking to each other.They work each other.They love each other.The men are helping each other.They're dancing with each other.问题:第一个句子为什么用了to,而第五个句子用了with?第2、3、4句为什么没用to或with?有什么规律或规则吗?