A customer list from a financial services company is shown below:

A data analyst wants to create a likely-to-buy score on a scale from 0 to 100, based on an average of the three numerical variables: number of credit cards, age, and income. Which of the following should the analyst do to the variables to ensure they all have the same weight in the score calculation?

A. Recode the variables.
B. Calculate the percentiles of the variables.
C. Calculate the standard deviations of the variables.
D. Normalize the variables.