Each family of functions has a parent function. A parent function is the simplest function that still satisfies the definition of a certain type of function.
A. this function is linear function;
B. This function is absolute value function and is known to be parent function, because it is of the simpliest form.
C. This function is also absolute value function, but is not of the simpliest form (parent function y=|x| is streched by factor 3 to form y=3|x|).
D. This function is quadratic function.
Answer: correct choice is B