The single quotation mark in front of the null list is used to tell Scheme that you are using as data and not as a part of your parse tree.

空列表前面的单引号用来告诉scheme您正在使用作为数据，而不是用它作为解析树的一部分。

youdao

Its most followed user, Mark Zuckerberg, now has more than 250, 000 followers, despite not Posting a single public item on his Google + account.

Google +上拥有粉丝最多的用户——马克·扎克伯格——现在已经拥有超过25万个粉丝，尽管他从来没在他的Google +账户上公开发布一条消息。

youdao

Kao Sung-nien's fat but firm face was like an unleavened millet-flour steamed bread. "Voracious time" (Edax vetustas) could not make a dent on it. There was not a single tooth mark or crease .

高校长肥而结实的脸像没发酵的黄面粉馒头，“馋嘴的时间”咬也咬不动他，一条牙齿印或皱纹都没有。

youdao

He filmed the beads of sweat provoked by the sun, probably even her pores although that smooth, uniform skin seemed to have no pores, no folds or bumps, and not a single stretch mark marred her buttocks.

NEWYORKER: While the Women Are Sleeping

Not a single song hits the four-minute mark.

NPR: The High Strung: 'Real Stone'