The current $I$ in a wire is defined as the derivative of the charge $Q;$ in other words, $I(t)=Q'(t).$ What does $\int_{a}^{\,b} {I(t)}\,dt$ represent?

A. The amount of current $I$ in the wire between time $t = a$ and $t = b$.
B. The total charge $Q$ at time $t = a$.
C. The total charge $Q$ at time $t = b$.
D. The change in the charge $Q$ from time $t = a$ to $t = b$.