先天发育缺陷所形成的肛门闭锁或肛门狭窄多发生于：（）
A.肛管直肠环
B.肛门白线
C.齿线
D.解剖肛管
E.外科肛管
参考答案：C
Many tall buildings _______ in Shanghai in the past few years.
A．has been built
B．have built
C．were built
D．have been built
磨煤机油泵出口滤网如何进行切换操作？
