After a cup of hot chocolate is poured, the temperature cools off very rapidly at first, and then cools off more slowly, until the temperature of the hot chocolate eventually reaches room temperature. Let $F(t)$ denote the temperature of the hot chocolate $t$ minutes after being poured.

(a) Based on this description, the function $F(t)$ is
A. increasing
B. decreasing
C. neither increasing nor decreasing
D. both increasing and decreasing

(b) Based on this description, the graph of the function $F(t)$ will be
A. Concave Up
B. Concave Down
C. Neither, it is linear
D. Both concave up and concave down