题目

Drowning (溺水) is among the 10 leading causes of death of children and young people in every region of the world, with children aged under 5 years especially at risk and males twice as likely to drown as females.Tragedies are happening over and over again. To prevent them from growing further, we need to keep some safety tips in mind. Remember, you can drown in the sea just as easily as a swimming pool.● Supervise when in or around Water.Ask a responsible adult to watch young children while in the bath and all children swimming or playing in or around water. Because drowning occurs quickl已知两定点F1，F2和一动点M，则“|MF1|+|MF2|=2a（2a为正常数）”是“点M的轨迹是以F1，F2为焦点的椭圆”的A.充要条件B.必要不充分条件C.充分不必要条件D.非充分非必要条件