When did Japan surrender?

Aafter the first atomic bomb was dropped
Bthe day the Soviet Union invaded Manchuria
Cthe day after Germany and Italy surrendered
Da few days after the second atomic bomb was dropped

By the time of the Yalta Conference, the Soviet Union had yet to declare war on Japan. What influenced Joseph Stalin to agree to enter the war against Japan?

AJapan attacked a naval base outside of St. Petersburg.
BThe Soviet Union felt Japan would be an easy ...