Which Has Not Been Suggested as a Reasonably Practical Way

Which has not been suggested as a reasonably practical way to store large amounts of hydrogen in relatively small spaces for its use as a fuel?

A) Liquefy hydrogen under pressure and store it much as we do with liquefied natural gas today.
B) Absorb hydrogen onto activated charcoal;then heat the mixture to release the hydrogen.
C) Store it in the form of ionic metal hydrides,such as LiH,which release hydrogen gas when they react with water.
D) Encapsulate hydrogen molecules in fullerene molecules (large,carbon-based molecules that can act like cages) that may be heated later to release the hydrogen.