I went there in 1984, and that was the only occasion when I was able to make the journey in exactly two days.
【翻译】1984年我去了那里，是唯一一次我能在两天内完成旅程的时候。

1. exactly 修饰数字 two，说明“正好两天”。常见的修饰数字的副词：

almost two days

about two days

nearly two days

over two days

around two days

approximately two days

roughly two days

2. was able to 不可以换为could。前者表示有能力且“成功做到”，后者只表示有能力，但不表示结果。详解如下；

（1）could表示“过去有能力做某事”，was able to 除了这层意思外，还有一个重要的意思，就是：“设法做了某事 (managed to do sth.)”，“成功地做了某事 (succeeded in doing sth.)”。如果只表达“有能力做某事”这层意思，不表示结果，两者可以互换，意思不变。例如：

He was very strong and he could (=was able to) lift the big stone. 他很强壮，他能够举起那块大石头。（只说明他有这个能力）

但是，如果是第二层意思，那么，只能用was able to，不能用could，例如：

The fire was very big，but most people were able to escape.（不用could）火很大，但多数人能够从火中逃出来。

At last he was able to solve the problem.（不用could）最后他终于解决了这个问题。

（2）在否定句中，could与was/were able to可以通用。

They were not able to/couldn't finish the task in such a short time.在这么短的时间里他们不能完成任务。

（3）与感知动词连用时，could与was/were able to可以通用。

The little boy could/was able to recognize his mother.那个小男孩能辨认他妈妈了。

I could/was able to see the tower in the distance. 我看见远处有座高塔。