Fact 1: Pneumonia may be caused by an infection or injury of the lungs.

Fact 2: Common bacterial pneumonia can be caused by Streptococcus pneumonia or Klebsiella pneumonia .

Given the two facts above, answer the question "injury of the lungs can be caused by what" with the following options: 
- running
 - wind and erosion
 - breathing
 - cigarettes
 - Pesticides
 - bacterial infection
 - smoking cigarettes
 - foggy air


 

      bacterial infection   