A:one needs to have profound knowledge
B:profound knowledge is important
C:profound knowledge is a must
D:it is required that one has profound knowledge
点P的直角坐标为(1,﹣3),则点P的极坐标为( )
被称为“天府之国”的成都平原,位于我国的哪个地区:
函数y=x4-4x+3在区间-2,3上的最小值为( )