四氯化碳灭火器使用于（）着火。
A.有碱金属存在的物质
B.有碱土金属存在的物质
C.电器
D.钠粉
参考答案：C
房地产开发企业应自工程竣工验收合格之日起（）日内，向工程所在地的县级以上地方人民政府建设行政主管部门备案。
A.20
B.7
C.15
D.12
We were sad to learn that several students were ____ by a car yesterday.
[ ]
A. hit out
B. knocked over
C. run across
D. picked up
