Patients with severe bacterial sepsis who develop a fever have higher survival rates than patients ...

Patients with severe bacterial sepsis who develop a fever have higher survival rates than patients with severe bacterial sepsis who do not develop a fever.
 
  Does this observation provide causative evidence for the beneficial role of fever in fighting infections?
  a. Yes, patients who develop a fever will have a higher mean fitness.
  b. Yes, developing a fever is correlated with a strong immune system.
  c. No, the disease in nonfever patients may have been too severe to allow the body to develop a fever.
  d. No, fever has been shown by other studies to be inconsequential in fighting infections.