Glutamate Can Be Toxic to Neurons Because​

Glutamate can be toxic to neurons because​ 

A) NMDA receptors allow calcium into a cell, and excess calcium can stimulate harmful levels of enzyme activity. 
B) NMDA receptors block the movement of calcium into a cell, preventing the release of other neurotransmitters. 
C) it blocks receptors for other types of neurotransmitters, preventing effective communication between cells. 
D) its breakdown in the synaptic gap produces harmful free radicals.