Respiratory tract infection, exposure to cold air, and emotional stress are all known triggers of:

The correct answer to your question is asthma attack:
- The asthma attack is triggered by respiratory tract infections like flu or pneumonia.
- The asthma attack is also triggered by cold due to the decrease in the diameter of bronchi.
 - Emotional stress is well known to cause an asthma attack.

Pneumonia is triggered by cold and respiratory tract infections but the emotional stress factor is not being proved yet.