**Core Concept**
ACE inhibitors are a class of medications that block the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, thereby reducing blood pressure. This mechanism involves the inhibition of angiotensin-converting enzyme (ACE), a metalloprotease responsible for catalyzing the conversion of angiotensin I to angiotensin II.

**Why the Correct Answer is Right**
The correct answer is B, as omitting the prior diuretic dose can indeed decrease the risk of postural hypotension when initiating ACE inhibitors. This is because diuretics can cause volume depletion, which can be exacerbated by ACE inhibitors, leading to a greater drop in blood pressure. By withholding the diuretic dose, the risk of severe hypotension is minimized, allowing the ACE inhibitor to take effect gradually. This is particularly relevant in patients who are already on diuretics and are being started on ACE inhibitors.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect because ACE inhibitors actually block the conversion of angiotensin I to angiotensin II, not the conversion of angiotensinogen to angiotensin I. Angiotensinogen is converted to angiotensin I by renin, not ACE.

**Option C:** This statement is incorrect because lisinopril is actually longer acting than enalapril. Lisinopril has a half-life of approximately 12 hours, whereas enalapril has a half-life of around 11 hours, but its active metabolite enalaprilat has a longer half-life of around 11 hours, making its overall duration of action longer.

**Option D:** This statement is incorrect because ACE inhibitors are actually beneficial in diabetic patients. They have been shown to reduce proteinuria, slow the progression of diabetic nephropathy, and decrease the risk of cardiovascular events in patients with diabetes.

**Clinical Pearl / High-Yield Fact**
When initiating ACE inhibitors in patients on diuretics, it is essential to omit the prior diuretic dose to minimize the risk of postural hypotension. This is a crucial clinical consideration to ensure safe and effective management of hypertension.

**✓ Correct Answer: B. Omission of prior diuretic dose decreases the risk of postural hypotension**