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.
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.
Interval scale data
Ordinal scale data
Categorical data
None