Is this
a. a function, but not one-to-one
b. a one-to-one function
c. not a function

The line does represent a function.

Moreover it's a one to one function because it passes the vertical test (a vertical line intersects the function in ONE and ONLY ONE point, so it's a function.

It's also a one to one function because it passes the HORIZONTAL line testr, so it's a ONE-TO-ONE function since the HORIZONTAL test intersects in one and only one point

It’s d for sure i just did also that’s why