#### Answer

(a) is increasing on the interval $(0, +\infty)$;
(b) has no interval where it is decreasing;
(c) constant on the interval $(-\infty, 0)$

#### Work Step by Step

Based on its graph, the given function:
(a) is increasing on the interval $(0, +\infty)$;
(b) has no interval where it is decreasing;
(c) constant on the interval $(-\infty, 0)$