**Core Concept**
The question is testing the understanding of managing hypertension crises in systemic sclerosis, a condition characterized by vascular damage and fibrosis. The underlying principle is the use of specific antihypertensive agents that can also counteract the pathophysiological mechanisms of systemic sclerosis.

**Why the Correct Answer is Right**
ACE inhibitors are the preferred choice for managing hypertension crises in systemic sclerosis due to their ability to block the angiotensin-converting enzyme (ACE), which is involved in the renin-angiotensin-aldosterone system (RAAS). Activation of the RAAS contributes to vascular fibrosis and endothelial dysfunction in systemic sclerosis. By inhibiting ACE, these drugs reduce the levels of angiotensin II, a potent vasoconstrictor, and aldosterone, a mineralocorticoid that promotes sodium retention and fluid overload. This mechanism helps to mitigate the cardiovascular and renal complications associated with systemic sclerosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Beta blockers are not the preferred choice for managing hypertension crises in systemic sclerosis as they do not address the underlying pathophysiological mechanisms of the disease, such as vascular fibrosis and endothelial dysfunction.

**Option B:** Losaan is not a commonly recognized antihypertensive medication, and its use is not supported by evidence in the management of systemic sclerosis.

**Option D:** Nitrates are vasodilators that can be used to manage acute hypertension, but they do not provide the long-term benefits of ACE inhibitors in systemic sclerosis, particularly in terms of reducing fibrosis and improving endothelial function.

**Clinical Pearl / High-Yield Fact**
It is essential to differentiate between systemic sclerosis and other conditions, such as scleroderma renal crisis, which requires aggressive management with ACE inhibitors to prevent renal failure.

**✓ Correct Answer: C. ACE inhibitor**