火车在某转弯处的规定行驶速度为v，则下列说法正确的是（　　）

A．当以速度v通过此转弯处时，火车所受的重力及轨道面的支持力这两个力的合力提供了转弯的向心力

B．当以速度v通过此转弯处时，火车所受的重力、轨道面的支持力及外轨对车轮轮缘的弹力这三个力的合力提供了转弯的向心力

C．当火车以大于v的速度通过此转弯处时，车轮轮缘会挤压外轨

D．当火车以小于v的速度通过此转弯处时，车轮轮缘会挤压外轨

—Why didn't you tell me the truth that day?

—I ________, but you ________ for Shanghai when I went to see you.[ ]

A. did; would leave  

B. would; had been away

C. would have; had left  

D. had; were away