The boy wanted to ride his bicycle in the street, but his mother told him ______.    [ ]

A. not to  

B. not to do  

C. not do it  

D. do not to

发现早期直肠癌最有效的方法是（）

A.直肠指诊

B.大便隐血

C.直肠镜

D.CEA

E.钡灌肠