对于8052单片机，当其引脚EA接高电平时，可扩展的外部程序存储器最大为（）k字节。
A.32
B.60
C.64
D.128
参考答案：B
Britain announced tighter security measures this week, with plans ______ full-body scanners at Heathrow airport within three weeks.
A．to use
B．to be using
C．being used
D．having used
鉴别H2、CO和CH4三种气体最好的方法是 [ ]
A．看颜色
B．嗅气味
C．分别通入紫色的石蕊试液
D．检验燃烧后的产物
