**Core Concept**
The question is testing the student's knowledge of potent vasoconstrictors used in clinical practice. Vasoconstrictors are substances that cause blood vessels to constrict or narrow, increasing blood pressure. In medicine, vasoconstrictors are often used to manage severe bleeding, shock, or during surgical procedures.

**Why the Correct Answer is Right**
The correct answer is **Norepinephrine**. Norepinephrine is a potent vasoconstrictor that acts on alpha-1 adrenergic receptors in the smooth muscle of blood vessels. This causes the blood vessels to constrict, increasing peripheral resistance and blood pressure. Norepinephrine is often used in intensive care units to manage severe hypotension or septic shock.

**Why Each Wrong Option is Incorrect**
**Option A:** **Option A is incorrect because it does not specify a vasoconstrictor.** While epinephrine is a catecholamine with vasoconstrictive properties, it is not as potent as norepinephrine.

**Option B:** **Option B is incorrect because it is a vasodilator.** Nitroglycerin is a nitrate that acts on smooth muscle to cause vasodilation, which would decrease blood pressure.

**Option C:** **Option C is incorrect because it is not a vasoconstrictor.** Dopamine is a catecholamine that can have various effects on the body, including vasodilation or vasoconstriction, depending on the dose and receptor subtype. However, it is not typically used as a vasoconstrictor.

**Option D:** **Option D is incorrect because it is not a vasoconstrictor.** Furosemide is a loop diuretic that increases urine production by inhibiting sodium reabsorption in the kidneys. It does not have vasoconstrictive properties.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that norepinephrine is a potent vasoconstrictor and should be used cautiously in patients with hypertension or cardiovascular disease. Additionally, norepinephrine can cause reflex bradycardia due to its vasoconstrictive effects, which can worsen cardiac output.

**Correct Answer:** C. Norepinephrine.