I really don’t know how to express my thanks to Mr. Li, my high school English teacher, without whose help I__________ to college that year.

A．weren’t to go

B．hadn’t been able to go

C．couldn’t go

D．couldn’t have gone

按钢的质量分类，主要根据钢中含碳量的多少来分，可分为普通钢和优质钢。