One way would be if all the trees were lined up in single file, such as on this island.

其中一种排法是如果所有的树都排成一条线，跟这座小岛的一样。

Then he set off very slowly, with the cygnets following along in single file. Their mother brought up the rear.

然后他慢慢地出发了，身后跟着排成一行的小天鹅。他们的妈妈跟在最后面。

At sundown they walked in single file into their pen.

日落时分，他们排成一列走进了他们的围栏。

I will go first, then you will come along in single file, and your devoted mother will bring up the rear.

我先走，你们排成一行跟着，深爱着你们的妈妈就在你们的后头。

He was thinking of swans' nests, and eggs, and the hatching of eggs, and the cygnets following their father in single file.

他正在想着天鹅的窝，鸟蛋，孵蛋的情景，还有那些跟着他们的父亲飞成一行的小天鹅们。

The latter fidgeted, but could do nothing but watch the birds fly in single file into the sky or fife all day.

后者为此坐立不安，但他什么也不能做，除了看鸟儿在空中成单行地飞行或是整天吹横笛。

Along this route Mr Beaver led them in single file right out to the middle where they could look a long way up the river and a long way down it.

海狸先生带着他们排成单行，往堤坝当中走去，在那儿他们可以看到上下游很远的地方。

We walked in single file, headed by the hunter, who ascended by narrow tracks, where two could not have gone abreast. There was therefore no room for conversation.

我们排成一列走，猎人带头，他沿着狭窄的小路向上走，两个人不可能并排走。因此，没有任何交谈的余地。

Not only did they have to remain silent at night, but when they walked in the day they marched in single file, locked to the prisoner in front of them.

他们不仅在晚上必须保持沉默， 而且在白天行走时，他们要排成一列， 紧紧盯着前面的囚犯。