For a continuous function f, suppose f(x)<0 for all 1<x<4. Define A(t)=∫0tf(x)dx. Which statement about A is true on the interval 1<t<4?
a) A\;is increasing throughout (1,4).
b) A\;attains an absolute minimum at t=4.
c) A\;is decreasing throughout (1,4).
d) A\;is decreasing and concave up on (1,4).