A.f(0)是f(x)的极小值. B.f(0)是f(x)的极大值. C.在点(0,f(0))的左侧邻近,曲线y=f(x)是凹的,右侧邻近是凸的. D.在点(0,f(0))的左侧邻近,曲线y=f(x)是凸的,右侧邻近是凹的.