A decomposition reaction causes a chemical to break apart into two products. You measure the rate of the reaction and find that it proceeds quickly at first, but slows down over time. How would you explain this result?
A. The concentration of the starting material decreases over time.
B. The concentrations of the products decrease over time.
C. The concentration of the starting material increases over time.
D. The rate of decomposition reactions doesn't change over time; there must be a measurement error.