One
I don't seem to be able to calculate the exact formula for this but the graph of it is below. It is not linear.
Two
y = x^3 is the graph for 2. It is not linear either.
Three
y = 2x - 1. This is a relationship that is linear. It does everything linear relationships should do.
Four
y = 2^x. This is not linear and there can't be two answers. So this isn't a choice