An Experimenter Conducts a Study in Which She Wants to Investigate

An experimenter conducts a study in which she wants to investigate the effects of eating chocolate on concentration.To do this she gives 20 people in an experimental condition a bar of chocolate and gives another 20 people in a control group nothing.After the experimental group has finished their chocolate she asks both groups to perform tasks designed to test their concentration.Which of the following statements is false?

A) The experiment has a within-subjects design.
B) The results could be analysed using a t-test.
C) The independent variable has two levels.
D) The dependent variable is level of concentration.
E) The addition of a control group controls for threats to internal validity.