Final answer:
The main complication of a lung infection with S. pneumoniae is C. Meningitis, which involves inflammation of the protective membranes of the brain and spinal cord.
Step-by-step explanation:
The main complication of a lung infection with Streptococcus pneumoniae (S. pneumoniae) is meningitis. This bacterial infection leads to inflammation of the meninges, which is the protective membrane covering the brain and spinal cord. It is important to note that S. pneumoniae can also cause other serious diseases such as septicemia, osteomyelitis, and endocarditis. But, when we consider complications specific to lung infection by S. pneumoniae, pneumococcal meningitis is a critical concern, especially in individuals with weakened immune systems.