5) A

Emphysema is a condition in which lungs and air sacs are damaged, causing breathlessness. 
Breathlessness is caused by shortage of oxygen.

If carbon monoxide reduces the supply of oxygen to the body cells, then this would cause emphysema. 
Carbon monoxide binds to the red blood cells and prevents the red blood cells from carrying oxygen to the body cells.

B – Wrong
Damage to cilia will not interfere with transport of oxygen

C – Wrong
Rapid growth of cells is called cancer not emphysema.

D – Wrong
Coughing cannot really cause emphysema.

E – Wrong
Irrelevant to breathlessness and inhibited oxygen transport.