Which best exemplifies the concept of neuroplasticity? a. the ability to use your arm to draw after the arm was severely broken b. the development of thicker heart muscles in old age after beginning an aerobic exercise class c. the production of large amounts of testosterone during puberty d. the formation of new brain cell connections as the result of reading a book?

The correct answer is "the formation of new brain cell connections as the result of reading a book".

Usually, neuroplasticity is apparent in young children when the central nervous system has an abundance of neurons. This is always in the context of forming new brain cell connections or synapses that will lead the person to access the information quicker. This also exemplifies the principle of use and disuse when it comes to knowledge. 

The other choices concerns the skeletal system, cardiovascular system, and the endocrine/reproductive system; all of which do not have a relation with neuroplasticity.

The answer to your question is vagina