Occasionally when I am writing a sentence, I end up in a situation where I do not know whether to use the singular or plural form of a noun because I used both just prior to it in a conjunction.
The worst, and one of the most common, problems is […]
One of the most common, and generally worst, problem is […]
Should problem be singular or plural in those sentences? Is there a rule for situations like this? (It certainly doesn’t help that for one of the most common problems is has is instead of are right next to a plural noun.)
Here is another example which (along with its non-contraction versions) does not fit the currently accepted answer.
In fact, the sentence before the above example with the parenthesized segment is itself confusing as to whether the next word should be does or do.