单纯性肛瘘只有内口而无外口者：（）
A.完全瘘
B.内口瘘
C.内盲瘘
D.外盲瘘
E.外口瘘
参考答案：C
We ______ go home now because it is too late.[ ]
A. can
B. may
C. have to
D. had to
主要纬向织疵有哪几类？其成因是什么？
