You Pay Respondents $10 at the Start of a Research

You pay respondents $10 at the start of a research study to increase participation.Vern,a respondent,wants to quit half-way through the survey.What is the appropriate course of action?

A) Allow Vern to quit and keep the $10
B) Allow Vern to quit but take back the $10
C) Try to talk Vern out of quitting,and tell him you will give him another $10 to continue
D) Try to talk Vern out of quitting,but provide no additional monetary incentive
E) Tell Vern that if he quits,he will need to pay a penalty of $5