Greg, Charlize, and Azarah run at different but constant speeds. Each pair ran a race on a track that measured 100\:m from start to finish. In the first race, when Azarah crossed the finish line, Charlize was 20\:m behind. In the second race, when Charlize crossed the finish line, Greg was 10\:m behind. In the third race, when Azarah crossed the finish line, how many metres was Greg behind?
Answer Choices
A. 20
B. 25
C. 28
D. 32
E. 40