What can be the main idea of the passage? ( )(本题2.5分)

A、 Two groups of people participated in an experiment.
B、 Light-colored rooms make students do better on the exams.
C、 People in nice-looking rooms tend to be biased in their opinion.
D、 The effects of a room’s general appearance and its wall color on visitors.
出自:西安石油大学-石油工程技术-大学英语l(下)