The slope-intercept form of the equation is noted as:

Where:
m = slope
b = y-intercept
Now looking at the 3 functions, we can see that they all have the same slope, however, they have different y-intercepts.
f(x)=2x
m = 2
b = 0
f(x)=2x+6
m = 2
b = 6
f(x)=2x-10
m = 2
b = -10
The best statement that would describe this would be C. They have the same slope but different intercepts.