DrVesner Is Examining How Exposure to Drug X Affects Levels

Multiple Choice

Dr.Vesner is examining how exposure to Drug X affects levels of aggression in rats.She gives each rat one of four doses of Drug X: no drug (saline injection) ,low dose,medium dose,and a high dose.After 20 minutes so the drug has time to take effect,she measures aggression by the intensity with which the rat bites a probing rod that is entered into the apparatus.In this study,what is the independent variable?

A) levels of aggression
B) dose of Drug X
C) 20-minute delay
D) intensity with which the rat bites a probing rod