Consider the Following Three Functions

Multiple Choice

Consider the following three functions:
g(x, y) = 4x - 3y + 21
H(x, y, z) = 13x² + y + 3z
I(z) = z
Which of the following is true regarding the linearity of the functions?

A) none of the functions is linear
B) all three functions are linear
C) h is linear, but g and i are not linear
D) i is linear, but g and h are not linear
E) g and i are linear, but h is not linear