问题
选择题
________twice a year，whether it is a car or a bus or a truck，is the rule that every driver must obey in this city.
A．Examining
B．Examined
C．Being examined
D．Having been examined
答案
答案：C
句中缺少的是主语，分词不作主语，故排除A、B项；从整个句子意思来看examine需要用被动式且用其一般式即可。