题目

 Jeff ________ the hospital if he feels better in a few days. A. leaves                 B. left                    C. will leave           D. has left    答案：C如图，已知双曲线y=（k＞0）经过Rt△OAB斜边OB的中点D，与直角边AB相交于点C．点A在x轴上．若△DOC的面积为3，则k=________．