Many people agree that___knowledge of English is a must in___internation trade today.为什么第一个要填a,第二个不填阿?

Many people agree that___knowledge of English is a must in___internation trade today.为什么第一个要填a,第二个不填阿?
Many people agree that___knowledge of English is a must in___internation trade today.
为什么第一个要填a,第二个不填阿?

Many people agree that___knowledge of English is a must in___internation trade today.为什么第一个要填a,第二个不填阿?
a knowledge of sth 是固定用法指对于某事的掌握.
第二个空若有冠词则是对于trade的,这里显然不能用a,而the也不对,因为它不是特指某商业交易.internation trade 内贸

knowledge前必须填a，因为后面的 must前有个a ，knowledge 和must指的是同一事物，必须一样。
第二个填the