When Teaching a Patient Who Is Starting Metformin (Glucophage), Which

When teaching a patient who is starting metformin (Glucophage) , which instruction by the nurse is correct?

A) "Take metformin if your blood glucose level is above 150 mg/dL."
B) "Take this 60 minutes after breakfast."
C) "Take the medication on an empty stomach 1 hour before meals."
D) "Take the medication with food to reduce gastrointestinal (GI) effects."