Which Statement About the Human Respiratory System Is True

Which statement about the human respiratory system is true?

A) Gas exchange occurs in the alveoli and in the small airways leading to them.
B) The thoracic cavity contains the lungs and is bounded by the ribs and the diaphragm.
C) The walls of bronchioles contain skeletal muscle.
D) Airways that conduct air to alveoli always contain fresh air.
E) Pleural membranes cover the lungs but do not line the thoracic cavity.