A dataset contains a categorical variable called Membership Status that has two levels: $(1)$ trial member and $(2)$ paid member. The Membership Status variable is assigned a O to indicate that a case represents a trial member and a $1$ to indicate that the case represents a paid member. What type of coding was used to assign values representing the diferent categories of this variable?O a$.$ indicator codingO b$.$ effects codingO c$.$ null codingO d$.$ unitary coding