North africa is bordered on the east by the sea.
a. black
c. red
b. mediterranean
d. caspian

To the East, North Africa is bordered by the Red Sea!
This is the sea separating for example Sudan from Saudi Arabia. The Mediterranean Sea is to the North of Africa and the Black sea is also in the direction of North, although it doesn't actually border Africa!

It is the doctrine that the us had the right and duty to expand throughout north america. it just means they believed they had the right to expand westward and they did! they stated with the 13 colonies and then they kept moving gaining different territories throughout the years

The answer is d., a mountain.