The event that happened FIRST among the options listed is:
D. PE becomes part of American school curriculum.
Physical education began to be formalized in American schools in the late 19th century, around the 1800s. The YMCA opened its first gym in America in 1851, but the formalization of PE in schools predates the establishment of the YMCA gym. The popularity of Nautilus trainers and elliptical trainers occurred much later.