How would you solve this? I am stuck between B and C but i may be incorrect. Thank you!

A store sold an item over a 16-month period. The total number of items sold up to time r is modeled by the twice-differentiable function S(7), where ? is the number of months since the store started selling the item. For the first 8 months, S' is increasing. After 8 months, S' is decreasing. Which of the following could be the graph of S(t) ? (A) S(I) (B) S(1) 8 12 16 (C) S(1) (D) S(t) 8 12 16 8 12 16