**Core Concept:**
Hypertension is a medical condition characterized by persistently elevated blood pressure values. It is classified into different grades based on the severity of the condition. The widely accepted classification system is the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC7).

**Why the Correct Answer is Right:**
According to the JNC7 guidelines, a patient with hypertension under control by medication is classified as Grade III hypertension. Grade III hypertension is defined as a systolic blood pressure of 180 mmHg or higher, or a diastolic blood pressure of 100 mmHg or higher. In this case, the patient's hypertension is under control (which means their blood pressure is within the normal range), so the correct answer is Grade III hypertension.

**Why Each Wrong Option is Incorrect:**
A. Grade I hypertension is characterized by a systolic blood pressure of 140-159 mmHg or a diastolic blood pressure of 90-99 mmHg. Since the patient's hypertension is under control, this option is incorrect.

B. Grade II hypertension is defined as a systolic blood pressure of 160-179 mmHg or a diastolic blood pressure of 100-109 mmHg. Similar to Option A, this option is incorrect because the patient's hypertension is under control.

C. Grade IV hypertension is characterized by a systolic blood pressure of 220 mmHg or higher, or a diastolic blood pressure of 110 mmHg or higher. This option is incorrect since the patient's hypertension is under control.

D. Grade V hypertension is defined as a systolic blood pressure of 220 mmHg or higher, or a diastolic blood pressure of 110 mmHg or higher. This option is incorrect as well because the patient's hypertension is under control.

**Clinical Pearls:**
1. Regular monitoring of blood pressure during treatment is crucial to ensure that patients with hypertension achieve and maintain optimal blood pressure levels within the normal range.
2. The JNC7 guidelines provide a standardized approach for defining hypertension grades, allowing healthcare providers to effectively manage and treat hypertension patients.

**Correct Answer:** D. Grade V hypertension is defined as a systolic blood pressure of 220 mmHg or higher, or a diastolic blood pressure of 110 mmHg or higher. Since the patient's hypertension is under control, the correct answer is Grade V hypertension.