The Cause of an Excessive Margin of Receptor Edge (Which

The cause of an excessive margin of receptor edge (which appears as a black band) on a nondiagnostic periapical image is

A) the edge of the receptor was not placed parallel to the incisal-occlusal surfaces of the teeth.
B) the receptor was not positioned in the patient's mouth to cover the apical regions of the teeth.
C) the receptor was underexposed.
D) the central ray was not directed through the interproximal spaces.