现代CPU中，几乎都采用指令流水结构，其特点是（）。

A.提高存储器存取速度

B.提高I/O处理速度

C.提高DMA传输速度

D.提高CPU运行速度

Had you come five minutes earlier, you（）the train to Birmingham. But now you missed it.

A.would catch

B.would have caught

C.could catch 

D.should catch