A．Their works were unsigned.
B．Many of their works were destroyed.
C．They never stayed in one place for a long time.
D．They worked for only a few years.

A．Why American industries grew rapidly in the nineteenth century.
B．How advances in transportation helped American cities develop.
C．Transportation between the cities of the United States.
D．Great American inventors of the nineteenth century.

A．It was no longer possible to keep horses.
B．It was difficult to find jobs.
C．They could no longer walk to work.
D．They had to pay more for their housing.