—How ­­­­­_____ you have been late then in such a small town?

—Lots of turns in the streets, and the buildings look all the same.

A．can

B．could

C．may

D．must

如果一个有效三段论的结论是全称肯定命题，则它的中项（）.

A.可以两次周延

B.可以两次不周延

C.不能两次都周延

D.不能一次周延，一次不周延

E.不能两次都不周延