x - y = 0
A, B, C, or D

Answer: D
Step-by-step explanation:
Using the equation y = mx + b.
m represents the slope
b represents where the line crosses the y axis.
We can attempt to set up the equation given in the same way.
x - y = 0
Add y to both sides and the 0 can drop out.
x = y
This is also equal to:
y = x
In this equation the m is equal to 1 and the b is equal to 0.
Taking this into account the answer is D.