Aresearcher wants to see if an aspirin advertisement increases sales if it uses a doctor spokesperson i instead of a kindergarten teacher spokesperson.
what is the independent variable?

Independent Variable :  The Person advertising

Explanation:

REGRESSION is statistical tool to analyse relationship between Independent Variable & Dependent Variable .

Independent Variable is the Variable causing change in the Dependent Variable & the Dependent Variable is the variable being affected by Independent Variable . Eg - In Law of demand price - demand inverse relationship (more price , less demand / less price , more demand) ; Price is the independent variable affecting dependent variable Demand .

In this case : Researcher is trying to analyse impact of advertising person on sales , so advertising person is independent variable & sales are dependent variable . However , regression analysis can be with quantitative (numerical) variables - so this qualitative variable can be converted into dummy variable (1 if person is a doctor , 0 if person is a teacher)

b is the correct answer