As $x$ varies from $-1$ to $+3$, which one of the following describes the behaviour of the function $f(x)=x^{3}-3x^{2}+1?$
- $f(x)$ increases monotonically.
- $f(x)$ increases, then decreases and increases again.
- $f(x)$ decreases, then increases and decreases again.
- $f(x)$ increases and then decreases.