If w'(t) is the rate of growth of a child in pounds per year, what does 8 w'(t)dt 6 represent?

A. The child's weight at age 8.
B. The child's weight at age 6.
C. The child's initial weight at birth.
D. The change in the child's weight (in pounds) between the ages of 6 and 8.
E. The change in the child's age (in years) between the ages of 6 and 8.