One Reason That Researchers Have Been Unable to "Read" Visual

One reason that researchers have been unable to "read" visual experiences using fMRI is that

A) fMRI gives too much data on neural activity.
B) fMRI gives us continuous information from visual perception.
C) fMRI is too slow and gives only static pictures of visual experience.
D) the signals measured by fMRI are collected from a limited number of neurons.