Rahul is serving as a research assistant. In the first phase of the experiment, Rahul gives each participant a can of cola or a can of caffeine-free cola. In the second phase of the experiment, Rahul...

Rahul is serving as a research assistant. In the first phase of the experiment, Rahul gives each participant a can of cola or a can of caffeine-free cola. In the second phase of the experiment, Rahul times the participants with a stopwatch while they play a video game. It sounds like this study is lacking a(n)

a. placebo control.

b. correlational design.

c. operational definition.

d. double-blind control.