Tom is a good boy. He often helps his mother______ housework.A. doing B. do C. did
下列关于乙醇的说法不正确的是
将等体积的苯、汽油和水在试管中充分混合后静置。下列图示现象正确的是
下列各组有机物只用一种试剂无法鉴别的是
二甲醚和乙醇是同分异构体,其鉴别可采用化学方法或物理方法,下列鉴别方法中不能对二者进行鉴别的是
下列根据实验操作和现象所得出的结论正确的是