Yesterday’s temperature at t hours past midnight was f(t) ^◦C. At noon the temperature was 20^◦C. The first derivative, f'(t), decreased all morning, reaching a low of 2^◦C∕hour at noon, then increased for the rest of the day. Which one of the following must be correct?
(a) The temperature fell in the morning and rose in the afternoon.
(b) At 1 pm the temperature was 18^◦C.
(c) At 1 pm the temperature was 22^◦C.
(d) The temperature was lower at noon than at any other time.
(e) The temperature rose all day.