To complete your statements regarding the equation \( y = 2x \):
A. The constant of proportionality is 2.
C. This is a proportional relationship because the y-intercept is 0.
This is correct because the equation \( y = 2x \) indicates that \( y \) is directly proportional to \( x \), with a constant of proportionality (or slope) of 2, and it passes through the origin (0,0), indicating that the y-intercept is 0.