In 1988 a Soviet icebreaking ship elped free thregray whales that had become trapped in the Arctic ice aftre they 【had s
问题描述：
In 1988 a Soviet icebreaking ship elped free thregray whales that had become trapped in the Arctic ice aftre they 【had swam】 into the coastal waters of Alaska ot feed.
这里错误是had swam应改为had swum,但这里两个过去完成时用after连接让我晕菜了,能这么用吗,after表示先后顺序,有一个是不是应该用过去式呢
答
有after就有时间的先后,在英语中以时态来体现.当然因为过去完成时就是英语中最“过去”的形式了,所以前后都是had done（那些鲸鱼被困已经用了had done,在此之前按理应该还要往前推一个时态,不过had done已经到顶了,所以他们游去阿拉斯加还是用的had done）.