A researcher is interested in whether circadian rhythms influence participants' performance on different kinds of memory tests. The researcher first classifies participants according to whether each is a morning person or an evening person. The researcher then randomly assigns participants to receive either an implicit memory test or an explicit memory test. The researcher then tests everyone at 8 A.M. What is(are) the main effect(s) being tested in the study?

A. memory test

B. type of person and performance

C. type of person and memory test

D. type of person