若数据3，-1，x，4，6的极差为8，则x=______．
根据题意：x-（-1）=8或6-x=8，
解得：x=7或x=-2．
故答案为：-2或7．
__________ her son for half a month, Marcia decided to leave for Texas with the hope of finding him.
A．Not heard from
B．Having not heard from
C．Not to hear from
D．Not having heard from
昆虫为了完成某一发育期所需总热量，称为（）。
A.热常数
B.发育起点温度
C.发育期平均温度
D.热辐
