A researcher investigates the relationship between blueberry consumption and cognitive performance among students by randomly assigning 20 students to consume a freeze-dried blueberry snack and 20 students to take a placebo snack for 2 months and then having students complete a cognitive assessment.

The response variable in this study is:

a.

Cognitive performance

b.

Freeze-dried blueberry snack (yes / no)

c.

Not enough information to tell