The derivative of a function g satisfies
g′(x)>0 for x<−1,
g′(x)<0 for −1<x<4, and
g′(x)>0 for x>4.
Which one of the following statements is correct?
a) g is decreasing on (−∞,−1)\;and\;(4,∞)
b) g is increasing on (−∞,−1)\;and\;(4,∞)
c) g is increasing on (−1,4)\;only
d) g is decreasing on (−∞,4)\;and\;increasing on\;(4,∞)