Why did japan open its ports to u. s. trade?
a.
to make a profit
c.
they feared a military attack
b.
to establish friendly relations
d.
to obtain opium

I believe the answer was, because they feared a military attack.

Japan at the time had an isolationist policy and very much wanted to be left alone. The United States essentially sailed over with warships asking to do trade. The 2nd time the US came back asking for an answer, they did so with an even larger military force.