________ you stepped into the lab with your shoes on? You’re supposed to take them off before you enter it. I told you so!

A．How come

B．How dare

C．How about

D．How long

大肠杆菌O157∶H7（）

A.是婴幼儿和旅游者腹泻的重要病原菌

B.主要引起类似菌痢的腹泻

C.不产生肠毒素，是婴儿腹泻的主要病原菌

D.引起出血性结肠炎、严重腹痛和血便

E.引起婴儿持续性水泻