Carlos was in a car accident and received a head injury that resulted in a decreased ability to produce speech. carlos has more than likely damaged his nervous system.

The brain is a part of the central nervous system together with the spinal chord.
The other part of the nervous system is the peripheral nervous system which is consisted of nerves and ganglions. 
Humans own their ability of speech to the three areas in the brain. 
Broca's area is essential for forming words, Wernicke's area helps us understand the meaning of words and the arcuate fasciculus connects these two areas and gives speech coherence. 

The awnser is b i believe