井下电气设备的三大保护是：短路保护、漏电保护、接地保护。
参考答案：错
等比数列{an}中已知a1+a2+a3=8，a4+a5+a6=-4，则S15=______．
People like to make friends with shares their interests．
A．whom
B．whomever
C．whoever
D．who
