Why Is It Difficult to Assign Specific Functional Roles to Glutamate

Multiple Choice

Why is it difficult to assign specific functional roles to glutamate, relative to other neurotransmitters?

A) Because it is found throughout the brain
B) Because it has very limited activity except in particular neural pathways
C) Because its inhibitory action on the cortex makes it difficult to interpret
D) Because it is not found in cortical neurons