—When Mum is at home, I have to practice every day, but she is on a business trip this week.
A:How often
B:How about
C:How much
D:How long
如图,在直角坐标系中,O为原点.点A在x轴的正半轴上,点B在y轴的正半轴上,tan∠OAB=2.二次函数y=x2+mx+2的图象经过点A,B,顶点为D.
They don't like .
如图是显微镜下观察到的人血涂片视野,下列说法正确的是( )