Question

冠词的英语改错题

Many people agree that knowledge of English is a must in international trade today.
哪错?why?

Answer 1

这是一道1996年的高考题。正确的说法是
Many people agree that a knowledge of English is a must in international trade today.

尽管knowledge是不可数名词,但有时可以加不定冠词,意为"对……有某种程度的了解。"
此处must也作名词，英语解释为：Something that is absolutely required or indispensable（绝对必要或不可避免的应当去做之事）例：
Promptness on the job is a must. Comfortable shoes are a must when taking a walking tour of Wales.
工作上准时是绝对必要的。步行去威尔士旅行时舒服的鞋是绝对必要的物品

Answer 2

must前面有必要加a么？must又不是名词，后面也不是一个做宾语的句子。