What is the energy source of this so-called solar-sail vehicle

A．had been abandoned by the Mayas about thirteen hundred years previously
B．had been occupied and developed by the Mayas about thirteen hundred years before
C．had been deserted by the Mayas as soon as the Spaniards arrived
D．was conquered by the Mayas thirteen hundred years ago

A．He remained in the saddle for several minutes spellbound.
B．He immediately jumped down and went forward.
C．He waited until his bed was ready and then dismounted.
D．He rode to the mound and stared at the structure before him.