Which is a precept of monotheism? a. meditation is necessary to achieve harmony with god. b. a supreme god fights against evil in the world. c. followers must obey proper dietary and moral principles. d. believers must live sparingly and modestly to honor god.

A - I don't think so. Meditation is necessary to achieve harmony with ourselves and/or the Universe (may be understood as God itself), but it's not crucial part of monotheism.

B - May be, but it's not always like that. Like in Christianity - there's a supreme god, but he doesn't fight against evil. Indeed he can get angry and punish people for the evil they make (the Great Flood is the greatest symbol of that)

C - It's common for nearly all religions as it helps keep people's faith under control, but still I don't think it's crucial for monotheism

D - Definitely yes - if there's one god, people should live in peace with him and do everything they can to make him happy.

So I'd rather pick only one answer - D.