Under what conditions can Karl Pearson’s correlation coefficient be…

Under what conditions can Karl Pearson’s correlation coefficient be calculated?

A. If the means of both the variables are equal
B. If one variable is measured on an interval scale and another is measured on an ordinal scale
C. If there is a linear relationship between two variables
D. If data are obtained in an interval or ratio scale for both the variables
E. If the direction of the relationship between two variables is known