A continuous function f satisfies f(t)>0 for 0<t<3, f(3)=0, and f(t)<0 for 3<t<8. Let F(x)=∫0xf(t)dt. Which statement about F on the interval (0,8) is true?
a) F is decreasing on (0,3) and increasing on (3,8).
b) F is increasing on (0,3) and on (3,8).
c) F is increasing on (0,3) and decreasing on (3,8).
d) F is decreasing on (0,3) and on (3,8).