Researchers Believe That the Conclusion of Myelin Growth Spurts in Areas

Researchers believe that the conclusion of myelin growth spurts in areas associated with language learning probably indicates​ 

A) the beginning of a period of enhanced language learning, as the brain is now mature enough to manage this new type of input. 
B) that a child will be mentally retarded, as learning will be adversely impacted. 
C) the onset of adulthood. 
D) the end of a critical period for language learning.