20世纪60年代，推动和支配摇滚乐坛的主要代表“披头士”乐队产生于（）国家。
A.美国
B.英国
C.法国
参考答案：B
Public relations practice is the deliberate , planned and sustained effort to establish and maintain mutual understanding between an organization and its public.
A．complete
B．related
C．intentional
D．active
隧道、人防工程、高温、有导电灰尘或灯具离地面高度低于2.5m等场所的照明，电源电压不应大于( )V。
A．42 B．36 C．24 D．12
