Polly recently started a new medication that is supposed to help her sleep more soundly. To determine if it's working, she keeps a sleep diary for 8 weeks so she can record how many times she wakes up during the night.

Which statement is true of this experiment?
A. The new medication is the response variable.
B. How many times she wakes up overnight is the response variable.
C. The duration of her experiment is the response variable.
D. How many times she wakes up overnight is the explanatory variable.