设平面区域,则 D绕y轴旋转所成旋转体体积为_____
则下列结论正确的是()
设f(x,y)在点(0,0)附近有定义,且,则
WeweretoldthatSuewouldbeidealforthejob,butshe________badlywhenwetalkedtoher.
SinceWilliamhadbeenseriouslyillforseveralmonths,hisparentswereworriedabout________toreturntoschoolfull-time.
Becareful,_______you'llfalldown.