Manifest destiny was the belief that
a. the united states should own most or all of north america.
b. slavery should extend westward beyond the south.
c. native americans had a right to the land they lost.
d. the united states should invade and capture all of mexico.

The answer is A.  The United States should own most of or all of America.  The Americans firmly believed that it was their destiny to expand throughout the American continent.  Eventually they accomplished that goal.  They later used Manifest Destiny as part of their reasons for their imperialists campaign.