Yesterday the teachers and students held a grand meeting _________ the 60th anniversary of our school.

A．in recognition of

B．in honour of

C．in celebration of

D．in possession of

螺旋桨桨叶的叶切面是指（）

A.桨叶与某一平面相切获得的剖面

B.桨叶与平行于轴线的某一平面相切获得的平面、

C.桨叶与圆柱面相切获得的剖面

D.桨叶与同轴圆柱面相切获得的剖面