According to the Diabetes Control and Complications Trial and the United Kingdom Prospective Diabetes study:

A. patients who improve their blood sugar control can reverse some of the complications of diabetes, such as neuropathy and retinopathy.
B. patients with sustained hyperglycemia are at increased risk of long-term complications of diabetes, such as vascular disease and nephropathy.
C. Patients with sustained hypoglycemia are at increased risk of infection because they have an impaired immune response and are more likely to have gastroparesis.
D. A and B.

D