In an Experiment to Examine the Effects of Sleep Deprivation

Multiple Choice

In an experiment to examine the effects of sleep deprivation on completion of a puzzle, one group is allowed to sleep eight hours while another group is made to stay awake. In this experiment, the independent variable is

A) the performance on the puzzle.
B) the amount of sleep each group was allowed.
C) the people who got eight hours of sleep.
D) the people who stayed awake.