challenge: What is a typical reaction used to prepare Grignard reagents that tolerates many functional groups?
  
  A. Treating a preformed Grignard reagent with an alkyl chloride
  B. Treating a preformed Grignard reagent with an aryl bromide or iodide
  C. Treating a preformed Grignard reagent with an aryl fluoride
  D. Treating a preformed Grignard reagent with an alkyl fluoride
  Answer: 