题目

—Whose new car is this? —It's ___________. It's __________second car. A . Mike and Tom's; theirs B . Mike's and Tom's; theirs C . Mike and Tom's; their D . Mike's and Tom's; their 答案：C点P在以F1、F2为焦点的双曲线x23-y29=1上运动，则△PF1F2的重心G的轨迹方程是 ．