Ophthalmologic examinations reveals blurred optic discs with indistinct margins

A 48 year old man presents to the emergency room with severe headache and blurred vision. His blood pressure is 230/140. Ophthalmologic examination reveals blurred optic discs with indistinct margins. An intravenous drip of sodium nitroprusside is started.
What is the mechanism of action of this medication?
A- Alpha adrenergic antagonist
B- Beta adrenergic antagonist
C- Ganglion blocker
D- ACE inhibitor
E- Direct smooth muscle vasodilator
Answer: https://goo.gl/ffFYxy

The answer is E, because Nitroprusside is a vasodilator that works by relaxing the muscles in your blood vessels to help them dilate (widen). This lowers blood pressure and allows blood to flow more easily through your veins and arteries.