它原指用纸做成的小卡片，正面问题背面答案。

Originally, this referred to a small paper card with a question written on one side and the answer on the other.

youdao

它原指用纸做成的小卡片，正面问题背面答案。

Originally, this referred to a small paper card with a question written on one side and the answer on the other.

youdao