There are times when you don't know how much of something there'll be. There can be
- only one of that thing, OR
- many of that thing.
The number isn't fixed. For example:
The officer/officers who had a hand in this robbery has/have not been found out yet. Police investigation is ongoing.
The student/students, a teacher is going to assist, attend/attends the ceremony with that teacher.
Writing like this can be strenuous and time-consuming. Is there a standard way to deal with this?
And moreover, there's also the trouble with the verb that directly follows it. What should the
beverb be — singular or plural? Note that I've avoided this issue in my examples.
Note: I don't know exactly what tags to use. If you edit, please add some explanation as to why you chose or removed a particular tag (...or tags).