Thomas is interested in variables that may affect an individual's athletic ability. He has people play soccer on a course in wet, dry, or icy conditions. In addition, Thomas has them play soccer with or without a warm-up session, and with athletic shoes or casual shoes. In this design, there are________ possible main effects and________ possible interactions.

a. 2; 3
b. 2; 2
c. 3; 12
d. 3; 4