Dental caries and gingivitis can be exacerbated not only by the foods patients eat but
also by when the patients eat them.
(A) not only by the foods patients eat but also by when the patients eat them
(B) by not only the foods patients eat but also by when the patients eat them
(C) not only by the foods patients eat but also by time when the foods are eaten
(D) by not only the foods that are eaten by patients but also by the times the foods are
eaten
(E) not only by what patients eat but also by when they eat it

OA: E

What does it refer to? I picked C only because of 'it' issue in E