—This photo makes me think of trip to the Great Wall last year.
—Yeah, we had a great time there.
A:a
B:an
C:the
D:/
I don't know ______.
在平面直角坐标系xOy中,抛物线y=﹣x2+2mx﹣m2+1的对称轴是直线x=1.
有机物种类繁多,性质变化复杂,下列关于有机物的说法错误的是( )