With Regard to Drug Metabolism, Which, If Any, of the Following

With regard to drug metabolism, which, if any, of the following statements, is true?
a) The therapeutic window is simply the range of plasma drug concentrations in which the drug has therapeutic benefit.
b) Each individual drug molecule is metabolized by a specific drug-metabolizing enzyme that is dedicated to the metabolism of that drug.
c) An ultrafast metabolizer is a person who metabolizes a drug too quickly and so is at risk of an overdose
d) A poor metabolizer is a person who cannot metabolize a drug properly and is at risk of an underdose.