**Core Concept**
Glycosylated hemoglobin (HbA1c) is a blood test that measures the average level of glucose attached to hemoglobin in red blood cells over the past 2-3 months. It is a key indicator of long-term glycemic control in diabetic patients.

**Why the Correct Answer is Right**
Good diabetic control is generally defined as an HbA1c level below 7%. This is because an HbA1c level of 7% or less indicates that the blood glucose levels have been well-controlled over the past 2-3 months, reducing the risk of diabetes-related complications. The American Diabetes Association recommends an HbA1c target of below 7% for most adults with diabetes. Levels between 7-9% may still be acceptable in some cases, but are generally considered less optimal.

**Why Each Wrong Option is Incorrect**
**Option A:** Levels above 9% are generally considered poor glycemic control, increasing the risk of diabetes-related complications.
**Option B:** An HbA1c level above 13% is indicative of very poor glycemic control and may require immediate medical attention.
**Option C:** Levels between 10-12% are generally considered suboptimal and may increase the risk of diabetes-related complications.

**Clinical Pearl / High-Yield Fact**
To remember the target HbA1c range, use the mnemonic "7 is sweet": an HbA1c level of 7% or less is generally considered good glycemic control.

**✓ Correct Answer: A. 7-9%**