H2S+I2═S+2H++2I中还原剂:H2S 还原产物:I-,还原性:H2S>I-,H2SO3+2H2S═3S↓+3H2O 还原剂:H2S 还原产物:S,还原性:H2S>S,2I-+Br2═I2+2Br- 还原剂:I- 还原产物:Br-,还原性:I->Br-,H2SO3+I2+H2O═4H++SO42-+2I-还原剂:H2SO3还原产物:2I-,还原性:H2SO3>I-,则还原性顺序:H2S>H2SO3>I->Br-,故选A.