The primary way in which a linear function stands out from other functions is that the independent variable, usually x, has the exponent 1: x^1 or just x.
Thus, we must immediately elimiinate A and C.
If you meant (1/3)x in B, then B is a linear function; if you meant 1 / (3x), then B is not a linear function.
Safest choice is D, supposing that by 2/3x=y-1 you actually meant
(2/3)x=y-1. You could solve this for y: y = (2/3)x + 1.
