the function is odd if you can replace every x with -x and get the oposite equation
example
if you replace x with -x in y=x^3, then you get -x^3, so therefor the functin is odd
so
replace x with -x
a. we get x^3+4, nope
b. we get -2x^3, yep
c. we get x^4-9, nope
d. we get x^4-4x, nope
answer is B
