Answer:D
When forming an equation of a line you always have y equals x so therefore it cannot be answer A or answer C.
The equation of a line is y=mx+c
M =the gradient and c= the y intercept
From the graph we can see the line intercepts the y axis at 0 so in this case c would be equal to 0.
The gradient is the change in y/ change in x. We can use the graph to help us.
Draw a triangle, like the one in pink. For the triangle in pink the change in y value is 2 and the change in x value is 4. Put this into the equation: 2/4 = 1/2 making the equation of the line y=1/2x