challenge: What was Charles Parsons primarily known for in the philosophical community?
  
  A. His work in the philosophy of mathematics and the study of Immanuel Kant's ideas
  B. His work in the philosophy of science and the study of Plato's ideas
  C. His contributions to the field of ethics and moral philosophy
  D. His research on the philosophy of language and the study of Friedrich Nietzsche's concepts
  Answer: 