The number line below represents which combined inequality?

Closed circle on -2, shading to the left, and closed circle on 4, shading to the right.

a: x is greater than or equal to -2 or x is less than or equal to 4.
b: x is greater than or equal to -2 and x is less than or equal to 4.
c: x is less than or equal to -2 or x is greater than or equal to 4.
d: x is less than or equal to -2 and x is greater than or equal to 4.