One Reason That the Visuospatial Sketchpad Is More Challenging to Study

One reason that the visuospatial sketchpad is more challenging to study than the phonological loop is that

A) it's difficult to find ecologically valid situations in which the visuospatial sketchpad is relevant.
B) participants are more likely to guess the correct answer, compared to studies that focus on the phonological loop.
C) participants may spontaneously provide a verbal label for a shape, so the task may actually use the phonological loop.
D) visual information must be presented more slowly than phonological information.