Why Did the Smooth Muscle in Cultured Strips of Aorta

Multiple Choice

Why did the smooth muscle in cultured strips of aorta not respond to acetylcholine by relaxing, while the smooth muscle of aortic rings did?

A) Smooth muscle cells in aortic strips are physically incapable of relaxing under any circumstances.
B) Acetylcholine in the strips could not penetrate to the muscle cells while in the rings it could.
C) Smooth muscle cells in aortic rings express acetylcholine receptors, while those in strips do not.
D) The delicate endothelial layer in aortal strips had been rubbed away during dissection, while in aortal rings it remained intact.
E) The endothelial layer in aortal strips was abnormally thickened, while in aortal rings it was not.