—She has ___________ a scientist for over thirty years.
A:played for
B:worked as
C:stayed with
下列实例中,利用物体惯性的是( )
元素周期表中氧元素的数据见如图,说法正确的是( )
函数y=mx2+x-2m(m是常数)的图像与x轴的交点个数为( )