美国副总统官邸准备加强安全装置。 "The Vice President's official residence is getting a $1.7 million security upgrade," 副总统官邸要进行耗资170万美元的保安系统升级。市场调查显示, "Many customers are putting off plans to upgrade their cell phones during the economic downturn," 经济不景气,使很多顾客推迟手机升级的计划。好的,今天我们学习的词upgrade...