The best answer is B) A land invasion would result in too many casualties.
The Japanese advance was halted as early as June 1942 with the Battle of Midway. The Americans fought slow, costly battles in New Guinea, then, in 1943, headed toward the Philippines. Fierce resistance at Iwo Jima and Okinawa and Japan’s refusal to surrender after the firebombing of Tokyo led the new president, Harry S. Truman, to order the use of the atomic bomb. Military planners had estimated that an invasion of Japan could cost as many as 250,000 Allied casualties and even more Japanese losses. Moreover, some 100,000 Allied prisoners of war being held in Japan would probably be executed when an invasion began. By that time, the firebombing of cities and the widespread killing of civilians had become accepted military practice. The use of atomic bombs on Japanese cities was thus seen as a logical next step to end the war.