英语提问：以下句子里的副词位置是否可以进行调换.
原句：The next morning we saw that the clock had stopped at exactly two a.m.
改句1：The next morning we saw that the clock had stopped exactly at two a.m.
改句2：The next morning we saw that the clock had exactly stopped at two a.m.
exactly的位置进行了如上调整,请问是否正确?如果正确这三句话里exactly又分别修饰什么词,有什么侧重点?