"aux." 是 助动词的缩写。在英语中，助动词是用来协助主要动词构成时态、语态、疑问句和否定句等语法结构的词。它们本身没有词汇意义，但具有语法意义。常用的助动词包括 "be", "have/has", "do/does", "shall", "did", "will", "should", "would", "can", "could" 等。
例如：
They donot want to work.
I didnot know Jamie had a knife.
Alex hasa knife.
在这些例子中，"do" 是助动词，用于构成否定句。