The derivative h′ of a differentiable function h has exactly two x-intercepts at x=−3 and x=1. The graph of h′ is positive on (−3,1) and negative on (−∞,−3) and (1,∞). Which of the following best describes the corresponding behavior of h?
a) h has a local maximum at x=−3 and a local minimum at x=1.
b) h has a local minimum at x=−3 and a local maximum at x=1.
c) h is decreasing on (−3,1) and increasing on (−∞,−3)∪(1,∞).
d) h is concave up on (−3,1) and concave down elsewhere.