微笑时的唇高线位于上颌中切牙的
A．切缘
B．切1/3
C．切1/2
D．切2/3
E．龈缘
参考答案：D
解析：微笑时的唇高线位于上颌中切牙的切2/3。
The split between humans and living apes is thought by some scholars _____ 15 to 20 million years ago. [ ]
A. to occur
B. occurring
C. to have occurred
D. having occurred
胃酸进入十二指肠后实现反馈抑制胃液分泌涉及的激素（）。
A.胃动素
B.胰泌素
C.胆汁
D.促胰液素
E.抑胃肽
