Small hair-like structures line the upper part of the human respiratory tract. These structures trap the dust particles, germs, and chemicals entering the human body during breathing. Smoking is likely to cause infections in the respiratory tract. Which statement best explains this fact?
$A$. Smoking destroys the hair-like structures.
$B$. Smoking causes excessive growth of the hair-like structures.
$C$. Smoking stimulates the hair-like structures to release harmful chemicals.
$D$. Smoking makes the hair-like structures wet and they fail to trap dust particles.

• A
  Smoking destroys the hair-like structures.
• B
  Smoking causes excessive growth of the hair-like structures.
• C
  Smoking stimulates the hair-like structures to release harmful chemicals.
• D
  Smoking makes the hair-like structures wet and they fail to trap dust particles.