challenge: What is the effect of grapefruit juice on nisoldipine concentrations in the body?
  
  A. Increases nisoldipine concentrations by inhibiting CYP3A4
  B. Has no effect on nisoldipine concentrations
  C. Reduces the metabolism of nisoldipine by 50%
  D. Decreases nisoldipine concentrations by 20%
  Answer: 