單項(xiàng)選擇題(2011)若函數(shù)f(x,y)在閉區(qū)域D上連續(xù),下列關(guān)于極值點(diǎn)的陳述中正確的是:()

A.f(x,y)的極值點(diǎn)一定是f(x,y)的駐點(diǎn)
B.如果P0是f(x,y)的集值點(diǎn)。P0點(diǎn)處B2-AC<0(其中,
C.如果P0是可微函數(shù)f(x,y)的極值點(diǎn),則在P0點(diǎn)處df=0
D.f(x,y)的最大值點(diǎn)一定是f(x,y)的極大值點(diǎn)