In each part, sketch the graph of a continuous function $f$ with the stated properties.
(a) $f$ is concave up on the interval $(-\infty,+\infty)$ and has exactly one relative extremum.
(b) $f$ is concave up on the interval $(-\infty,+\infty)$ and has no relative extrema.
(c) The function $f$ has exactly two relative extrema on the interval $(-\infty,+\infty),$ and $f(x) \rightarrow+\infty$ as $x \rightarrow+\infty$
(d) The function $f$ has exactly two relative extrema on the interval $(-\infty,+\infty),$ and $f(x) \rightarrow-\infty$ as $x \rightarrow+\infty$