A mental health plan in high schools used a questionnaire asking about the frequency of the experience of several negative mental health states in students on a numerical scale, from 1 = 'rarely experienced' to 5 = 'frequently experienced'. The scores were summed and a cut off score was established regarding the presence or absence of symptoms. This is a(n):

a)Nominal variable.

b)Ratio variable.

c)Interval variable.

d)Ordinal variable.