Which of these is not one of the American Triple Crown horse races?

The Arlington Million is not one of the American Triple Crown horse races. It is a Grade 1 flat horse race in the United States for thoroughbred horses aged three years and upward. It is raced annually in August over a distance of 1 1⁄4 miles (approximately 2,000 metres) on the turf at Arlington Park in Arlington Heights, Illinois. The Arlington Million was the first thoroughbred race to offer a purse of US$1,000,000. It is part of the Breeders' Cup Challenge series, and the winner automatically qualifies for the Longines Breeders' Cup Turf.

In the United States, the Triple Crown of Thoroughbred Racing, commonly known as the Triple Crown, is a title awarded to a three-year-old Thoroughbred horse who wins the Kentucky Derby, Preakness Stakes, and Belmont Stakes. The three races were inaugurated in different years, the last being the Kentucky Derby in 1875. These races are now run annually in May and early June of each year. The Triple Crown Trophy, commissioned in 1950 but awarded to all previous winners as well as those after 1950, is awarded to a Triple Crown winner.