Which single sentence most precisely defines a one-to-one function (injective)?

A graph consists of the parabola $y=x^2$ and the line $y=2$. Using vertical and horizontal line tests, determine whether the parabola is a function, whether it is one-to-one, and whether its restriction x ≥ 0 is one-to-one. Provide justification.

A graph is the sideways parabola $x=y^2-1$ (opening to the right). Decide whether its inverse $x\leftrightarrow y$ describes a function, and justify using a line test.

A function $f$ maps temperatures in Celsius to voltages measured by a sensor: $f=\left\{\right(0,0.00),(25,0.50),(50,1.05),(75,1.65\left)\right\}$. The inverse function $f^{-1}$ is used to convert voltage back to temperature. What problem occurs when trying to evaluate $f^{-1}\left(2.00\right)$?

A graph displays a continuous increasing curve that starts at $(-3,0)$ and rises strictly monotonically to $(3,6)$. Which statements are true? Explain.

(I) Passes vertical line test

(II) Passes horizontal line test

(III) Has an inverse that is a function on the interval $[0,6]$