Answer:
The correct option is a. "increased cortical mass, increased numbers of neurons, increased synaptic connections, increased neurotransmitter amounts, and increased myelination. "
Step-by-step explanation:
Rodents that have been raised in enriched environments were found to have thicker cerebral cortex containing approximately 25% more synapses in a study conducted by Mark Richard Rosenzweig. This increase in synapses implies in an increase in neurons and neurotransmitters, which also indicates an increase in myelination.