一弯曲等截面直杆，横截面积为Ａ，截面m-m的外向法线n与n的夹角为α。试问α位多大时，m-m截面上剪应力最大？该截面上剪应力与正应力分别为多少______

A.α=－45° Ｔ =p/A

B.α=45° Ｔ =p/A ζ=p/2A

C.α=45° Ｔ =p/A ζ=p/2A

D.α=45° Ｔ =p/2A ζ=p/A

E.