Properties of Parametric Arc Length

I. The arc length of a parametric curve for $a \le t \le b$ is given by the formula $\int_{a}^{b} \sqrt{(dx/dt)^2 + (dy/dt)^2}\,dt$.

II. In the arc length formula, if the derivatives $dx/dt$ and $dy/dt$ are positive, it is not necessary to square them.

III. The limits of integration, $a$ and $b$, are the parameter values corresponding to the endpoints of the curve.

Which of the above statements are true?