一船在静水中的速度为6m/s，要横渡河宽60m，水流速为8m/s的河，下面说法正

已知数列{a_n}的前n项和S_n=pⁿ+q（p≠0且p≠1），求证q=-1是数列{a_n}成等比数列的充要条件．

配电箱内应设置漏电保护器，其额定漏电动作电流和额定漏电动作时间应安全可靠。总配电箱内的漏电保护器，额定漏电动作电流与额定漏电时间的乘积最高应限制在()mA·s内。

A．30
B．45
C．60
D．75

皮样与表皮样囊肿的区别是

A．表皮样囊肿不含角化物

B．皮样囊肿不含角化物

C．皮样囊肿的囊壁不含皮肤附件

D．皮样囊肿含一种或多种皮肤附件

E．表皮样囊肿的囊壁含皮肤附件

社会发展的决定力量是( )。

A．地理环境
B．人口
C．物质资料的生产方式
D．阶级斗争

For each blank, choose the best answer from the four choices and write down on the answer sheet.
(66) is a six bytes OSI layer 2 address which is burned into every networking device that provides its unique identity for point to point communication.
(67) is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.
(68) functions with two layers of protocols. It can connect networks of different speeds and can be adapted to an environment as it expands.
(69) is the popular LAN developed under the direction of the IEEE 802.5.
(70) is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.

A．The hub

B．The bridge

C．The router

D．The proxy