In preparing categorical variables for analysis, it is usually best to a. combine as many categories as possible. b. convert the categories to numeric representations. c. let them remain categorical.

In the given question the correct option is missing, which can be described as follows:

"It transforms binary, null variables into the groups."

Explanation:

These variables are real variables, which could also take up a series of variables, that are either constrained or defined. This can be regarded as a listing. It is used to analyze and convert it, into binary in the following ways, and wrong choices can be described as follows: