题目

下列物质分别与NaOH的醇溶液共热后，能发生消去反应，且生成的有机物不存在同分异构体的是 答案：B _________ in the car, the president waved to the crowd, when _________ the _________ street． [　　] A． Sitting; passed; crowded B． Seated; passing; crowded C． Sat; passing; crowding D． Seating; passed; crowding