Research examining the think-drink effect gave some participants a nonalcoholic drink, some a weak ...

Research examining the think-drink effect gave some participants a nonalcoholic drink, some a weak alcohol drink, and some a strong alcohol drink to see how aggressive they would be.
 
  The participants were also told how much alcohol they were getting, but the researchers did not necessarily tell them the truth about the amount. What is(are) the independent variable(s)?
  a. amount of aggression
  b. amount of alcohol received
  c. amount of alcohol they were told was in the drink
  d. both the amount of alcohol they received and the amount of alcohol they were told was in the drink