4. 表示职位或头衔的抽象名词作
表语、宾补、主补或
同位语时其前一般不用冠词。但表示具体的人时要用
定冠词the。
as mayor of San Antonio 作为
圣安东尼奥的市长， mayor作为as的表语，且是职位，所以不用冠词。 had had a mayor from ，这是泛指的，所以也要用冠词a。
谢谢 希望我说得不乱 望采纳
以下是不用冠词的情况：
1. 人名、街名、公园名、大学名、国名前一般不用冠词。
Wangfujing Street; Pei Hai Park; PekingUniversity
2. 抽象名词表示一般概念时一般不用冠词。
When you finish reading the book, you will have a better understanding of life. （辽宁2004）
3. 物质名词表示泛指或一般概念时一般不用冠词。
The warmth of the sweater will of course be determined by the sort of wool used.(全国2001)
4. 表示职位或头衔的抽象名词作表语、宾补、主补或同位语时其前一般不用冠词。但表示具体的人时要用定冠词the。
We will elect Engineer Liu director of our factory. 类似的名词还有：president, monitor, headmaster, mayor等。
5. 在表示季节、月份、星期、节假日等的时间名词前不用冠词。但我国的阴历节前常用定冠词the。
in summer; in October; Children’s Day; Women’s Day; May Day; the Spring Festival
6. 在表示三餐、学科名称、球类活动和棋类游戏的名称前不用冠词。
have breakfast; play basketball; play chess
He majors in English.
7. man 作“人类”讲时，同 human或mankind 一样不用冠词。
While he was investigating ways to improve the telescope, Newton made a discovery, which completely changed man’s understanding of color. (广东2004)
8. by与表示通讯或交通手段的词连用时不用冠词。
If you go by train, you can have quite a comfortable journey, but make sure you get a fast one. (全国III卷2005)
9. 复数名词前不用冠词，泛指类别。
It is often said that teachers have a very easy life. (北京2005)
10. 有些名词与介词搭配表示抽象意义，不用冠词，常作状语。
His daughter is always shy in public and she never dares to make a speech to the public.（上海2001）
in surprise / wonder / danger / tears /comfort / love; under pressure; beyond expression
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4. 表示职位或头衔的抽象名词作表语、宾补、主补或同位语时其前一般不用冠词。但表示具体的人时要用定冠词the。
as mayor of San Antonio 作为圣安东尼奥的市长， mayor作为as的表语，且是职位，所以不用冠词。 had had a mayor from ，这是泛指的，且可数，所以要用冠词a。