Answer:
The spleen acts as a filter for blood as part of the immune system. It also helps fight against certain kinds of bacteria that cause pneumonia and meningitis.
A minimum point used for comparison i think
The theme is the writer's view of or comment about the subject. The answer to your question is D. I hope this is the answer that you are looking for and it comes to your help.
Out of the options I would have to say Penetrating Keratoplasty, I am not sure
