Final answer:
In a multi-row variable set, the variable that is not supported is D. Label, because it does not accept user input being a form descriptor or heading.
Step-by-step explanation:
The variable that is NOT supported within a multi-row variable set is D. Label. Multi-row variable sets are used in ServiceNow and are designed to allow users to input multiple sets of data, each row containing its own set of variables.
Options such as Email, Wide Single Line Text, and Multi Line Text are types of input fields that users can fill out with different values. However, Label is used as a descriptor or heading within forms and does not take an input from the user, hence, it's not considered an interactive variable within the context of a multi-row set.