Let $f : \mathbb{R} \rightarrow \mathbb{R}^{2}$ be a function given by $f(x) = (x^{m}, x^{n})$, where $x \in \mathbb{R}$ and $m, n$ are fixed positive integers. Suppose that $f$ is one-one. Then\\
(a) Both $n$ and $m$ must be odd\\
(b) At least one of $m$ and $n$ must be odd\\
(c) Exactly one of $m$ and $n$ must be odd\\
(d) Neither $m$ nor $n$ can be odd.