In the question, data has been divided into two groups, i.e. HIV positive/HIV negative Data should be measured on nominal scale especially Dichotomous type of nominal scale.
Interval scale data
Ordinal scale data
Categorical data
None
Ans. is 'c' i.e., Categorical data Blood group is a qualitative (Categorical) data. Blood group are divided into qualitative categories (A, B, AB, 0) -3 Nominal Scale Data.