There were mainly ______ types of family in the United States in the late 18OOs and early 1900s.

A．A family where grandparents, parents and children live under the same roof.
B．A family only with parents and children.
C．A family including two couples without children.
D．A family where the children live alone, not together with their parents.

A．it was very durable
B．the tools and weapons were made of stone
C．there was little vegetation
D．the people lived in caves