For a relation to be a function, each element on the input group (Domain) has to be related to a single element on the output group (Range). To determine which of the options are not functions, we need to look for one that violates this rule.
The first option violates this rule, because the elements 1 and 2 from the input group are related to the element 5 in the output group. The correct answer is A.
3.4m questions
4.4m answers