单项选择题
A.[49.92,51.88] B.[49.7,51.88] C.[50.6,51.88] D.[49.92,51.1]
A.f'>0,f">0 B.f'<0,S"<0 C.f'<0,f">0 D.f'>0,f"<0
A.364 B.750 C.3310 D.154