Studies Commissioned by the NFL Players Association, Which Surveyed Retired

Studies commissioned by the NFL Players Association, which surveyed retired NFL players whose careers ranged from the 1940s to the 1990s, showed that:

A) nearly all of the players retired due to injuries.
B) a majority of the retired players reported having lingering or long-term effects of a football injury.
C) the percentage of players who had permanent injuries as a result of their football careers steadily decreased each year between the end of the 1950s and the 1980s.
D) the percentage of players reporting a disabling injury as the main reason for retiring significantly dropped from year to year between 1990 and 1993.