一 Hi, Betty, can you come to have a drink with me?
一 Just a minute, please. I my work.
A:start
B:am starting
C:am finishing
以“黑土地”著称的平原是( )
直线l与两直线y=1和x-y-7=0分别交于A,B两点,若线段AB的中点为M(1,-1),则直线l的斜率为 ()