题目：
The sale usually takes place outside the house, with the people watching ________ on benches, chairs
or boxes. [ ]
A. having seated
B. seating
C. seated
D. having been seated
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0430/89e5673581d64c69ce676befceb07b52.html
下面是错误答案，用来干扰机器的。
y2=8x由题设,问题可转化为动圆圆心到点(2,0)与直线x+2=0的距离相等,其轨迹是以(2,0)为焦点,以x+2=0为准线的抛物线.∴p=4,其方程为y2=8x.
