Below, There Are Several Statements About Measuring Complex Social Variables

Below, there are several statements about measuring complex social variables like racial bias. Which one of these statements is INCORRECT?

A) There is no one perfect way to measure a complex social variable like racial bias.
B) It is best to measure such variables on a scale from "completely disagree" to "completely agree".
C) Measuring such variables through direct observation of behavior is often difficult and has serious limitations.
D) Survey responses about variables like racial bias may be skewed by social desirability.