Which of the Following Is an Example of "Amount of Variable

Which of the following is an example of "amount of variable" variation of the independent variable?

A) All participants' response times are measured after eating sweets
B) In a study of distraction on problem-solving ability, one group is distracted by noise, another by a flashing light, and a third by a bad odor
C) The control group gets 1 minute to solve a problem, one experimental group gets 2 minutes, and a second experimental group gets 5 minutes to solve the problem.
D) An experimental group receives 5 mg/kg of a drug and the control group receives no drug.