How did the romantic concerto differ from earlier types of concertos?
they were longer
they placed more emphasis on virtuosity throuhgout the piece
placed greater amphasis on the orchestra
featured more improvisation by the soloist

The right answer is B, as in the Romantic period virtuosity developed enormously. It was more versatile, bright and impressive. However, it should be mentioned that all the contrasting ideas were impossible to express succinctly, so romantic concertos were mostly longer than classical ones. Also, the role of orchestra increased significantly. It was opposed to the hero, soloist. In previous concerts the interaction soloist-orchestra was just a competition, while in the romantic concertos it was a supreme opposition and conflict. Regarding the last answer, it is also true in some extent, as the soloist in romantic concertos had more freedom and opportunities for improvisation.