At the midpoint of the bridge she stopped. 在桥的中点处她停了下来。
Then we discuss the necessary conditions for the limit curve to be C0,C1,C2 respectively and give the derivative and second derivative of the limit curve at vertex and midpoint. 随后我们讨论了极限曲线连续，一阶连续，二阶连续的必要条件，并给出了极限曲线在顶点以及中点处的一阶导数与二阶导数显式公式。
