\textbf{108.} The function $f(x) = x^2\sqrt{x}$ is one-to-one on a domain. Which of the following is the inverse function on this domain?
(1) $-\sqrt{x^2}\ ,\ x \leq 0$ \qquad (2) $-\sqrt[3]{x}\ ,\ x \leq 0$ \qquad (3) $-\sqrt{x^2}\ ,\ x \geq 0$ \qquad (4) $-\sqrt[3]{x}\ ,\ x \geq 0$