Convert a protein prescription of 1.2 g/kg/day for a 70-kg adult into milligrams per day.

84,000 mg/day.

840 mg/day, because milligrams are always 100 times smaller than grams in dietary conversions for macronutrients.

8,400 mg/day, obtained by dividing the gram total by 10, which is correct for mass-to-mass conversion in nutritional contexts.

1,200 mg/day, derived from multiplying body weight by 1.2 without converting units, which is accurate for kilograms to milligrams conversion.