Only when _______ home_____ that he had left his bag in the taxi he had taken.

A．he returned; did he realize

B．did he return; did he realize

C．he returned; he realized

D．did he return; he realized

用酸性KMnO₄溶液不能达到预期目的的是

A．区别苯和甲苯

B．检验硫酸铁溶液中是否有硫酸亚铁

C．检验CH₂=CHCHO中含碳碳双键

D．区别SO₂和CO₂