The vertex of a parabola is at (-2,4) and the x-intercepts are at -6 and 2. Determine the domain and range of the function.

a. D: all real numbers
R: all real numbers

b. D: -6 ≤ x ≤ 2
R: y ≤ 4

c. D: all real numbers
R: y ≤ 4

d. D:x ≤ 4
R: all real numbers