A patient was taking 310 mg of antidepressant each day. However, the doctor determined that his dosage was too high and reduced the dosage by a fifth. Further observation revealed the dose was still too high, so he reduced it again by 20 mg. What is the final dosage of the patient's antidepressant
A. 20 mg
B. 42 mg
C. 228 mg
D. 248 mg