Which of the Following Is a Drawback of Behavioral Measures

Which of the following is a drawback of behavioral measures in psychological research?

A) Researchers lack clear insight of participants' behavior.
B) People may modify their behavior if they know they are being observed or measured.
C) Researchers need specialized training on expensive equipment, on how to collect measurements, and on data interpretation.
D) Behavioral measures are more susceptible to social desirability bias than are self-report measures.