I actually did get this one right ;)  and then i looked it up to be sure, because i couldn't remember the exact reason that it was in my head that WWII had ended the depression....

But, i think WWII is the correct answer.  first of all it's a mulitple choice question and you have to choose the best of the answers, but secondly, it created the jobs (supply & demand) that the economy desperately needed. it may have been on it's way to being healed slowly but surely prior to the outbreak of the war, but it was the war that put an end to it once and for all.

I highlighted the basis for my answer in red, taken from the wikipedia link you provided, under the "recession' headline.

By 1936, all the main economic indicators had regained the levels of the late 1920s, except for unemployment, which remained high. In 1937, the American economy unexpectedly fell, lasting through most of 1938. Production declined sharply, as did profits and employment. Unemployment jumped from 14.3% in 1937 to 19.0% in 1938. The Roosevelt Administration reacted by launching a rhetorical campaign against monopoly power, which was cast as the cause of the depression, and appointing Thurman Arnold to act; Arnold was not effective, and the attack ended once World War II began and corporate energies had to be directed to winning the war. By 1939, the effects of the 1937 recession had disappeared.

Employment in private sector factories recovered to the level of the late 1920s by 1937, but did not grow much bigger until the war came and manufacturing employment leaped from 11 million in 1940 to 18 million in 1943. Another response to the 1937 deepening of the Great Depression had more tangible results. Ignoring the pleas of the Treasury Department, Roosevelt embarked on an antidote to the depression, reluctantly abandoning his efforts to balance the budget and launching a $5 billion spending program in the spring of 1938, in an effort to increase mass purchasing power. Business-oriented observers explained the recession and recovery in very different terms from the Keynesians. They argued the New Deal had been very hostile to business expansion in 1935–37, had encouraged massive strikes which fiscal stimulus required to end the downturn of the Depression was, and it led, at the time, to fears that as soon as America demobilized, it would return to Depression conditions and industrial output would fall to its pre-war levels. The incorrect Keynesian prediction of a new depression would start after the war failed^{[citation needed]} to take account of pent-up consumer demand as a result of the Depression and World War.hj

Analaya79 Sep. 27, 2008 at 1:06 AM