For a Producer of Joint Products X and Y with Total

For a producer of joint products X and Y with total costs C_X and C_Y,an isocost curve:

A) isolates C_X and C_Y separately.
B) shows points where C_X = C_Y .
C) shows points where cost curves are tangent.
D) shows points where C_X /C_Y is constant.
E) shows points where C_X + C_Y is constant.