Researchers Interested in How Sleep Deprivation Affected Performance Randomly Assigned

Researchers interested in how sleep deprivation affected performance randomly assigned participants to groups that had one, two, or three nights of sleep deprivation. Then they tested their reaction times on a standard motor reaction task.The dependent variable in this experiment was:

A) the amount of sleep deprivation each group was subjected to.
B) how much sleep each group needed following the sleep deprivation experiment.
C) the reaction times of the three groups on the standard motor reaction task.
D) how often the participants fell asleep during the sleep deprivation phase of the experiment.