Lewis has agreed to proofread a long legal brief that Trudy has written, even though he doesn't really like Trudy. Lewis knows that he will not be paid anything extra for his work and thinks that proofreading is one of the most boring jobs there is. However, after the legal brief is finished, Lewis decides that proofreading isn't such a bad job after all and he feels that he actually enjoyed the work. The change in attitude that Lewis has experienced can BEST be explained using:

a. the matching hypothesis.
b. the fundamental attribution error.
c. a self-serving bias.
d. cognitive dissonance theory.