The Sport Journal (Winter 2004) reported on a study of a speed-training program for high school football players. Each participant was timed in a 40-yard sprint both before and after training. The researchers measured two variables: (1) the difference between the before and after sprint times (in seconds), and (2) the category of improvement ("improved," "no change," and "worse") for each player. What is the type for the variable "improvement"?

A. Ordinal
B. Interval
C. Ratio
D. Nominal