应该说葛老的说法没有错，我个人学习的体会是如果名词使用单数，是指复数主语中的每一个人各自的情形。这也是现代英语中常见的现象。你的问题句就是指他们每人各自的职业。这里职业是可数名词单数，当然用复数也可以。请看例句：

A bigger challenge happens when your children are old enough to want — or insist upon — riding their own bike, but still too slow or weak to ride long distances quickly.

All students, staff and faculty at the University of Cincinnati are asked to register their bicycle with the Department of Public Safety.

This online development portal is available to all UC faculty, academic personnel, staff and students seeking to advance their career.

For women who are looking to advance their careers, following these ten tips is a step in the right direction.