Which of the Following Is an Example of "Present Versus

Multiple Choice

Which of the following is an example of "present versus absence" variation of the independent variable?

A) All participants' reaction times are measured after ingesting two beers
B) In a study of distraction on reading comprehension, one group is distracted by noise, another by a flashing light, and a third by a bad odor
C) The control group gets no drug, one experimental group gets 5 mg/kg of a drug, and a second experimental group gets 10 mg/kg of the drug
D) An experimental group receives 5 mg/kg of a drug and the control group receives no drug (placebo)