Select a response.
The best response to the query is C. They are feeling worthless or hopeless.
A non-observable warning sign refers to a sign or symptom of a mental health condition that cannot be easily seen or detected by others.
On the other hand, Option C (They are feeling worthless or hopeless) describes internal feelings that are not outwardly visible and cannot be perceived or observed by others; these emotions exist within the individual and require them to express them verbally for others to understand. Thus, it is a true non-observable warning sign of potential mental health struggles.