题目

Humans have sewn by hand for thousands of years. It was said that the first thread was made from animal muscle and sinew (腱). And the earliest needles were made from bones. Since those early days, many people have been involved in the process of developing a machine that could do the same thing more quickly and with greater efficiency. Charles Wiesenthal, who was born in Germany, designed and received a patent（专利权） on a double-pointed needle that eliminated(消除) the need to turn the needle around with each stitch (缝合) in England in 1755. Other inventors of that time t已知离心率为2的双曲线x22-y2b2=1(b＞0)的左右焦点分别为F1，F2，且点P(3，1)在曲线上，则PF1?PF2=（　　）A、-12B、-2C、0D、4