How many separate cost pools should be formed given the following information?

$$

$$ Cost$$ Cost driver

$$ Postage costs$$ # of brochures mailed

$$ Printing and paper costs$$ # of brochures mailed

$$ Quality control costs$$ # of inspections

$$ Customer service costs$$ # of customers served

$$

Question $20$ options:

$4$ cost pools

$1$ cost pool

$2$ cost pools

$3$ cost pools