Which of the following is NOT a true statement about compressed air energy storage for transportation in comparison with using batteries to power an electric vehicle? a. The energy density that can be achieved in a compressed air system is much less than that for currently available advanced batteries. b. Recharging the fuel supply in the vehicle can be done very quickly. c. The energy density that can be achieved in a compressed air system is comparable (at best) to rather low-tech batteries. d. Compressed air systems use toxic materials. e. Compressed air systems use straightforward technology