Consider the following types of vehicles: I. Full battery electric vehicles II. Hydrogen fuel cell vehicles III. Fuel cell-electric hybrid vehicles. How many of the above are considered as alternative powertrain vehicles?

• I. Full battery electric vehicles: These use an electric motor powered by rechargeable batteries instead of a conventional internal combustion engine. Verdict: Correct; they are alternative powertrain vehicles.
• II. Hydrogen fuel cell vehicles: These generate electricity onboard from hydrogen in a fuel cell to run an electric motor. Verdict: Correct; they are alternative powertrain vehicles.
• III. Fuel cell-electric hybrid vehicles: These combine a fuel cell system with battery/electric drive components for propulsion. Verdict: Correct; they are also alternative powertrain vehicles.

Hence, all three are alternative powertrain vehicles.