若一个多边形的内角和为720°，则其对角线的条数为______．
（n-2）•180°=720°，故n=6．
该多边形为六边形，所以对角线条数为9条．
《素问.脉要精微论》认为“骨将惫”具备下列症状（）。
A.转摇不能
B.不能久立
C.屈伸不能
D.行则偻附
E.行则振掉
---- How long was it ______ you finally reached your goal of becoming a doctor?
---- Five years.
A．before
B．since
C．when
D．until
