题目

若函数y=3x3-9x+a有两个零点，则实数a= . 答案：±6 【解析】由y'=9x2-9>0，得x>1或x<-1，所以当x=1时，y极小值=a-6；当x=-1时，y极大值=a+6，所以a-6=0或a+6=0，所以a=±6.Much to our _________, Sam wasn’t _________ at the _________ news. A．surprise; surprised; surprise               B．surprise; surprised; surprising C．surprised; surprising; surprised             D．surprising; surprised; surprise