为什么用that不用which引导定语从句？

【问】

In 2017, Li Ziqi uploaded her first video on YouTube ____ was about how to make a dress using the skins of grapes.

答案：that

是不是用which也可以？

【答】

在定语从句中，当指“物”的先行词有序数词修饰时，通常用that而不是which指代。本句先行词video有first修饰，所以用that不用which。

类似的用that不用which的情况还有：

1. 最高级修饰先行词，如：This is the best film that I have even seen.
2. any、only、ever等修饰先行词，如：It was the only novel that I read before school.
3. 先行词是不定代词，如：We used anything that we could find to make candles to see the words.

特别需要注意的是，当先行词是“人”时，无上述限制，用that或who/whom均可。如：

• He is the only person that/whom I believe in.