Answer: Choice A
Proof:
Replace x with 1 and y with 2. This is because (x,y) = (1,2) so x = 1 and y = 2.
Doing both replacements and simplifying leads to...
2*x - y = 0
2*1 - 2 = 0
2 - 2 = 0
0 = 0
That confirms (x,y) = (1,2) is a point on the line.
It confirms (1,2) is a solution to the equation.