The correct answer is A.
You have direct variation if x and y are modeled by the equation
[tex] y = mx [/tex]
In this case, m is the constant of proportionality. So, if the constant has to be 2, the equation becomes
[tex] y = 2x [/tex]
A side note: Actually, option C has a constant of proportionality of two as well, except the roles of x and y are interchanged. I chose option A because usually you want the y = mx form, but the names of the variables are obviously meaningless.
