Helen ______ with her class if she had been able to meet all of the course requirements in time.
【正确答案】 B
【答案解析】从句中用了过去完成时had been able to，根据句意可看出，这是对过去事实的虚拟，事实上，海伦当时没有完成课程要求，所以她当时就未能毕业。可见，“毕业”这一动作本应在过去已经完成的，故用“would+have graduated”，答案为B。