下颌第一恒磨牙最小的牙尖是 （）
A.远中舌尖
B.近中舌尖
C.近中颊尖
D.远中颊尖
E.远中尖
参考答案：E
He was busy writing a story, only ______ once in a while to smoke a cigarette.
A．to stop
B．stopping
C．to have stopped
D．having stopped
