表示与众不同的职位（如 chairman, president, captain 等）作表语时，到底前面能否用冠词，有些书上说不能用，而有些书上又说可用可不需要。我想请问一下，有没比较权威的说法？
你说的状况在不少语法书确实有点“乱”，助你找到一个权威的说法。以下材料引自著名语法学家夸克等人合著的《英语语法大全》：
There is, however, one circumstance in which the zeroarticle occurs in such constructions: this is wherethe complement namesa UNIQUE ROLE or task. As the following examples show, in such cases thezero article alternates with the:
但在如下的状况下，这类结构中出现零冠词，即句子的补语（或相应的同位语名词短语）是某一个与众不同的身份或职务的名字。下列例句表明，在这样的情况下零冠词与the可以交替用：
Maureen is captain of the team.
John F. Kennedy was President of the United States in 1961.
As chairman of the committee, I declare this meeting closed.
They’ve appointed Fred treasurer, and no doubt he will soon become secretary.
Anne Martin, star of the TV series and author of a well-known book on international cuisine, has resigned from her post on the Consumer Council.
依据夸克等人的《英语语法大全》，你说的这样的情况中的冠词是可有可无的（并非必须要省略）。
