someone knocked( )the door while i( )my houseworka.at,were doingb.at,was doingc.on,was doingd.on,were doing

相关推荐

• someone knocked( )the door while i( )my houseworka.at,were doingb.at,was doingc.on,was doingd.on,were doing
• The policeman came up to the lonely house,whose door was open,____there for a whilehe policeman came up to the lonely house,whose door was open,____there for a while ,and then entered itA to stand B standC stoodD standing
• While two detectives were keeping guard at the door请问这里的guard at the door是固定搭配吗?