How did the size of the us changed from 1776 to 1870? ?

In 1776 the us comprised od 13 colonies.By 1870  U.S. had expanded beyond the Mississippi river to the states of Minnesota,Nebraska and Texas.Oklahoma was still a territory. The U.S had the states of California,Nevada and Oregon on the west coast.Territories were between the west coast states and the states beyond the Mississippi river.

It's most likely choice a, it makes the most sense in my opinion.

Basically create a schedule on what you need to study and stick with it