What is the domain of the function shown in the mapping?
A.) {x | x = –5, –3, 1, 2, 6}
B.) {y | y = –9, –6, 0, 2, 4}
C.) {x | x = –9, –6, –5, –3, 0, 1, 2, 4, 6}
D.) {y | y = –9, –6, –5, –3, 0, 1, 2, 4, 6}