Which piecewise relation defines a function?

A. y = [ x², x < -2
[ 0, -2 < x < 4
[ -x², x > 4

B. y = [ x², x < -2
[ 4, -2 < x < 4
[ x² + 1, x > 2

C. y = [ -3x, x < -2
[ 3, 0 < x < 4
[ 2x, x > 4

D. y = [ -3x, x < -4
[ 3, -5 < x < 1
[2x, x > 1