challenge: What is one method to prepare Lithium hexafluorostannate?
  
  A. Reacting ammonium hexachlorostannate, lithium carbonate, and fluorine gas at 400 °C
  B. Reacting lithium stannate with nitric acid
  C. Reacting lithium carbonate with hydrochloric acid
  D. Reacting lithium stannate with sulfuric acid
  Answer: 