由于产氢细菌的存在,使氢(H2)能部分地从废水中逸出，导致有机物内能下降,所以在产酸阶段，废水的COD值有所（ ）

A、Mn3＋ 和 Mn2＋
B、Mn3＋ 和 MnO42－
C、Mn3＋ 和 MnO2
D、MnO2和 MnO42-

de the reservation at the airport. After he arrived and checked in at the hotel, he filled out a registration card and got the key to his room. His room number was 235. Breakfast was included in the bill, which was served for several hours in the morning. Tom would pay for the hotel cost when he checked out. The receptionist hoped that he would enjoy himself during his stay there.Tom Johnson came to a【11】. He wanted to stay in a single room with bath. He made the reservation at the【12】. After he arrived and checked in at the hotel, he filled out a registration card and got the key to his room. His room number was 235. Breakfast was included in the【13】, which was served for several hours in the morning. Tom would【14】for the hotel cost when he checked out. The receptionist hoped that he would【15】himself during his stay there.