At about what age does the brain begin “pruning”?

From ages 3-16 it is the most rapid, and gradually slows down.

Different areas of the brain undergo pruning at different times. She is right though it is from 3-16. 

Bmust be the answer, as technically all organs move, so a is incorrect. all organs are made of different types of cells, so that isn’t a problem, so c is also incorrect. human hearts are very similar to many other animals’ hearts, so d is also incorrect, yet the heart is made of muscle, which is hard to grow in the lab so it would be correct to say b