In the respiratory system certain structures allow air to pass from the trachea to the lungs. They are lined with thin muscles and coated with epithelial cells. These structures are called A. bronchial tubes.
B. alveoli.
C. bronchioles.
D. lobules.

d ) power this is the right answer

it's false.

"every person has their limitations which prevent us from accomplishing something. some are better than mathematics for example and some are worse. those people who are worse might never be able to become mathematicians, but that does not mean that they would not be great at doing something else."

well when looking at this if you think about it   negativley and positivley   react with each other and when the first layer gets full they add layers it starts with 2 on the first layer and it constantly goes on until the official number is there