challenge: What is the effect of spironolactone on the glucocorticoid receptor (GR)?
  
  A. It has no effect on the GR at any concentration
  B. It strongly binds to and acts as an inverse agonist of the GR
  C. It strongly binds to and acts as an agonist of the GR
  D. It weakly binds to and acts as an antagonist of the GR
  Answer: 