--- Is her sister a teacher or a student?
--- .
A:No, she's a teacher
B:No, she isn't a teacher
C:She's a student
D:Yes, she's a teacher
①AD=DC;②AB=BD;③AB= BC;④BD=CD,
其中正确的个数为( )
在生物实验设计中,下列不能作为一组对照的是( )
已知一个碳原子上连有两个羟基时,易发生下列转化: 。请根据下图回答问题: