Honshu, Kyushu and Shikoku are three of Japan's four main islands. What is the fourth?

Along with rattlesnakes and copperheads, which venomous pit viper is native to the United States? Which actor won an Oscar for his role in 1974's "The Godfather Part II"? Which of these countries borders Thailand? Oddly, which country's flag was NOT among the four displayed on the summit of Mount Everest on May 29, 1953? In December 1944, Marshall, MacArthur, Eisenhower and which air commander became the first U.S. Army five-star generals? Which of these was one of the four original U.S. cabinet posts under George Washington? Which dentist fought alongside the Earp brothers against the Clanton gang at the O.K. Corral on October 26, 1881? Which of these was one of the four original provinces of Canada at Confederation in 1867?