已知椭圆的焦点是F1、F2,P是椭圆上的一个动点,如果延长F1P到Q,使得|PQ|=|PF2|,那么动点Q的轨迹是[ ]
A.圆
B.椭圆
C.双曲线的一支
D.抛物线
答案:A
Cross-sectional returns studies contend that:()
A. all securities should have equal risk-adjusted returns because security prices should reflect all public information that would influence the security’s risk.
B. all securities should have equal risk-adjusted returns because security prices should not reflect all public information that would influence the security’s risk.
C. securities should not have equal risk-adjusted returns because security prices should not reflect all public information that would influence the security’s risk.
周期性健康检查的优点()。
A.在具体时间内了解危险因素
B.对无症状人群进行早发现、早治疗
C.对高危人群的针对性检查
D.可节约卫生资源
E.有较好的社会效益