问题：
_____ 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
_____ 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
A. Examining
B. Examined
C. Being examined
D. Having been examined
参考答案：