A Magazine Article on Preventing Cancer Says, "Eating One Serving

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests."
The data come from an observational study; therefore,

A) the results must be false.
B) the results must be true.
C) there may be lurking variables.
D) perhaps those who chose to eat more tofu are, for some reason, less susceptible to breast cancer than those who didn't.
E) Both C and D are correct.