在正式写作中，直接引语必须用引号括起来。

In formal writing, direct speech must be enclosed in ___quotation ___marks.

在美式英语中，直接引用总是使用双引号。

Always use double ___quotation ___marks for a direct quote in American English.

术语‘人工智能’在首次提及时常常放在引号中。

The term 'artificial intelligence' is often placed in ___quotation ___marks when first introduced.