______ for the free tickets, I would not have gone to see films so often.

A．If it is not

B．Had it not been

C．Were it not

D．If they were not

某总线在一个总线周期中并行传送4个字节的数据，假设一个总线周期等于一个时钟周期，总线时钟频率为66MHz，求总线带宽是多少？