What effect does frequency have on wave height?

Maglev trains float on a cushion of air, eliminating friction. this lack of friction and the trains' aerodynamic designs allow these trains to reach unprecedented ground transportation speeds of more than 310 mph (500 kph). developers say that maglev trains will eventually link cities that are up to 1,000 miles (1,609 km) apart. at 310 mph, you could travel from paris to rome in just over two hours. magnetic levitation (maglev) trains use electricity to generate magnetic fields. how are these magnetic fields related to the forward motion of the train? a) electricity is used to generate a magnetic field opposite that of the train so the train is pulled forward along a frictionless surface. b) electricity is used to generate a magnetic field of the same polarity as that at the base of the train. this elevates the train and also moves it forward. c) electricity generates a magnetic field as it flows through coils on the train. a large electromagnetic at the opposite end of the track pulls the train to its destination and lifts it off the track. d) a current below the train generates a magnetic field that levitates the train, by using the repulsion of like charges. electricity flows through coils on the side of the track, as the current alternates it pulls the train forward and pushes it from the back.