In each part, sketch the graph of a function $f$ with the stated properties.
(a) $f$ is increasing on $(-\infty,+\infty),$ has an inflection point at the origin, and is concave up on $(0,+\infty)$
(b) $f$ is increasing on $(-\infty,+\infty),$ has an inflection point at the origin, and is concave down on $(0,+\infty) .$
(c) $f$ is decreasing on $(-\infty,+\infty),$ has an inflection point at the origin, and is concave up on $(0,+\infty) .$
(d) $f$ is decreasing on $(-\infty,+\infty),$ has an inflection point at the origin, and is concave down on $(0,+\infty) .$