5. The benefit of measuring the initial rate of a reaction V0 is that at the beginning of a reaction: (A) [ES] can be measured accurately. (B) varying [S] has no effect on V0. (C) changes in Km are negligible, so Km can be treated as a constant. (D) V0 = Vmax. (E) changes in [S] are negligible, so [S] can be treated as a constant.