The Consumer's Demand Curve Can Be Obtained Analytically by Solving $M U _ { x } / M U _ { y } = P _ { x } / P _ { y } ; U = \bar { U }$

The consumer's demand curve can be obtained analytically by solving which two equations?

A) $M U _ { x } / M U _ { y } = P _ { x } / P _ { y } ; U = \bar { U }$ where $\bar { U }$ is the initial level of utility.
B) $M U _ { x } / M U _ { y } = P _ { x } / P _ { y } ; P _ { x } X + P _ { y } Y = I$
C) $P _ { x } X + P _ { y } Y = I$ ; $U = \bar { U }$ where $\bar { U }$ is the initial level of utility.
D) $M U _ { x } / M U _ { y } = P _ { x } / P _ { y } ; U = \bar { U }$ where $\bar { U }$ is the final level of utility.