Amy has long _____________. [ ]
A. hair
B. hairs
C. a hair
答案：A
通常计数器应具有____功能。
A．清零、置数
B．存、取数码
C．放大功能
D．无记忆功能
Keep the door ______. It's too cold outside. [ ]
A. closing
B. closed
C. to close
D. open
