Let $f\;:\;R\rightarrow R$ be defined by $f(x)\;=\;\frac{1}{x}\quad x\;\in\; R.$Then f is

Question

$$\begin{array}{1 1}(A)\;one-one & (B)\;onto \\(C)\;bijective & (D)\; f \;is\; not\; defined\end{array}$$