A huge amount of poisonous chemical waste is dumped into the river, so the river is seriously contaminated. * 1 điểm A A huge amount of poisonous chemical waste is dumped into the river; however, the river is seriously contaminated. B The river is seriously contaminated; as a result, a huge amount of poisonous chemical waste is dumped into the river. C The river is seriously contaminated; moreover, a huge amount of poisonous chemical waste is dumped into the river. D A huge amount of poisonous chemical waste is dumped into the river; therefore, the river is seriously contaminated.