Consider the Following Three Functions

Multiple Choice

Consider the following three functions:
g(x, y) = 4x - 9y²
H(x, y, z) = 13x + y + 3z -6
I(y, z) = z - y
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) h and i are linear, but g is not linear