\textbf{Which of the following is/are categorical variable(s)?}  \textbf{I. The mean of Grade 1 boys' heights}  \textbf{II. The colors of jackets in the class}  \textbf{III. The types of pens in a stationary store} 
选项为:A:I  B:II  C:III  D:I, II  E:II, III  请回答其中一个选项.