The teacher wants his students _________ hard. [ ]
A. work
B. works
C. working
D. to work
答案:D
肛管直肠周围脓肿常继发于
A.肛裂B.肛窦炎C.嵌顿性内痔D.直肠息肉继发感染
风险的属性是什么?