Which of the following statements about air irritants is true?

• A. Air irritants are only produced by microorganisms.
• B. Air irritants are always non-toxic and do not affect human health.
• C. Air irritants are only found in outdoor environments.
• D. Air irritants can cause inflammation of respiratory tissues and may promote microbial infections.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the term 'air irritants' — these are substances in the air that can cause irritation to the respiratory system, including the nose, throat, and lungs.
2. Step 2: Recognize that air irritants can originate from multiple sources, including microorganisms, chemical pollutants, and physical particles, so they are not produced only by microorganisms.
3. Step 3: Know that air irritants can be toxic or non-toxic, but many have the potential to cause inflammation and negatively impact human health, so the statement that they are always non-toxic is incorrect.
4. Step 4: Realize that air irritants are present in both outdoor and indoor environments, such as pollution outdoors and dust or mold indoors, so they are not limited to outdoor environments.
5. Step 5: Conclude that the true statement is that air irritants can cause inflammation of respiratory tissues and may promote microbial infections, as inflammation can weaken the respiratory defenses and allow infections to take hold.