英文中职务前冠词问题

正职或表示独一无二的官衔，职位，称号”的专有名词作表语、补语、介词的宾语或同位语时，前一般不加冠词：
The guards took the American to General Lee. 士兵们把这个美国人送到李将军那里。
Lincoln, president of the United States, was murdered in 1864.
In 1860, Lincoln became President of the United States.
We made him head of our class.
但这个名词后有短语“of”时，有时也可加“the”：
He is (the) captain of the basketball team. 他是篮球队的队长。
He is chairman of the Students’ Union. 他是学生会主席。
They elected him president of the U.S. 他们选他当美国总统。
如不是独一的要加不定冠词：
She is a teacher of English in our school. 她是我校的一位英语教师。