Which of the following participants is more likely to experience the John Henry Effect?

Select one:

a. John overhears that he is in the experimental group and will ingest caffeine and not a placebo. This motivates him to run faster because he knows he has an edge. 

b. Mark knows he is being observed so he tries to complete the puzzle as fast as he can.

c. Anna overhears the test administrator say she hopes participants in the red shirts run faster than the participants in the green shirts. Anna has been given a green shirt and now wonders if she should run slower to make the researcher happy. 

d. Mary overhears that she is in the control group and is motivated to try even harder.