"Spies never sleep."
Translation:not Qong ghoqwI'.
The plural markers are optional. That means that in many situations the unmarked noun could be interpreted as either singular or plural. Usually the context makes it clear whether you meant it to be singular or plural. However, if you need to make it clear that you are talking about multiple of the noun, then the plural markers are available for that. The lack of context here on Duolingo usually means we will accept it either way.