单选题 The major goal of USB was to define an external expansion bus which makes adding (71) to a PC as easy as hooking up a telephone to a wall-jack. USB 2.0 is an evolution of the USB 1.1 (72) , providing a higher performance interface.

【正确答案】 A
【答案解析】
【正确答案】 B
【答案解析】试题71-72[分析]
USB的主要目的是用来定义外部扩展总线，使外设添加到PC上变得更加容易，就如装配一个电话到墙壁插座上一样。USB 2．0是USB 1．1规格的升级，它提供一个高性能的接口。