i want to ask : is it a, b, c or d?

In a world that is about to face an energy crisis, the planes will be fuelled by solar energy. Solar panes will be fitted on the exterior of the planes. Solar energy is not only non-flammable but also free as it is provided by the sun. The speed of the planes will also improve greatly. Aeroplanes will fly faster, allowing their passengers to reach their destination in a shorter time.