Which of These Situations Would Be Least Vulnerable to the Social

Which of these situations would be least vulnerable to the social desirability bias?

A) You ask therapists whether they believe their treatment of clients for anxiety is usually effective.
B) You conduct a client satisfaction survey where clients respond to questions anonymously.
C) You ask a client in a therapy session if he or she believes the therapy is helping.
D) You give a group of clients the Beck Depression Inventory before and after therapy and they respond anonymously.