For a Producer of Joint Products X and Y with Total

For a producer of joint products X and Y with total revenue and R_Y,an isorevenue curve:

A) isolates R_X and R_Y separately.
B) shows points where R_X = R_Y .
C) shows points where revenue curves are tangent.
D) shows points where R_X /R_Y is constant.
E) shows points where R_X + R_Y is constant.