请问下列句子表达方式有错吗?
1.whentheygottothemiddleoftheriver.
2.whentheyreachedthemiddleoftheriver.
3.whentheyarrivedtothemeddleoftheriver.
4.whentheywereinthemeddleoftheriver.
5.whentheycametothemeddleoftheriver.
6.whentheyswamtothemeddleoftheriver
邮箱:联系方式: