The temperature T (in ∘C) of a chemical solution is a differentiable function of time t (in minutes). At t=7 min it is observed that T′(7)=−0.6. Which statement best describes the behaviour of the temperature at that instant?
a) The temperature is constant.
b) The temperature is increasing at 0.6∘C per minute.
c) The temperature is decreasing at 0.6∘C per minute.
d) The temperature is decreasing at 6∘C per minute.