challenge: What is the primary function of the nine older, non-cytotoxic drugs used in the CUSP9 cancer treatment protocol?
  
  A. To directly kill glioblastoma cells with cytotoxic effects
  B. To block growth factors that enhance or drive glioblastoma growth
  C. To stimulate the immune system to attack cancer cells
  D. To enhance the effectiveness of traditional cancer cell killing drugs
  Answer: 