You are presented with the question "Pneumonia may be caused by viruses or " and the following answer choices: 
- bacteria
 - a hazard
 - cold weather
 - humidity
 - mildew
 - PDAs
 - injury
 - methane

Now knowing that pneumonia may be caused by an infection or injury of the lungs and infections of the lungs can be caused by bacteria, viruses or fungi, choose the best answer.


 

       injury  