You are presented with the quiz "injury of the lungs can be caused by what" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "pneumonia may be caused by an infection or injury of the lungs" and "common bacterial pneumonia can be caused by Streptococcus pneumonia or Klebsiella pneumonia ". 

So, what's the best answer to the question?


 

      bacterial infection     