【单选题】
We often get ____ when people cut in line.
【单选题】
“Can I help you?” “Well, I’m afraid the box is too heavy for you, ____ thank you all the same.”
【单选题】
A guest arrived ____ I was doing my housework.
【单选题】
—OK, $ 500, but that is my last offer. —____.?
【判断题】
空间曲线必穿过法平面和从切平面,但不穿过切平面.
【简答题】
求圆柱螺线x=acost,y=asint,z=bt的曲率和挠率
【简答题】
求正螺面r(u,v)={ucosv,usinv,v}在(0,0)处的高斯曲率和平均曲率