英语问题the old lady’s hand shook

英语问题the old lady's hand shook
1.The old lady's hand shook frequently.She explained to her doctor_____this shaking had begun half a year before,and ____,only because of this,she had been forced to give up her job.
A.when ; how
B.how ; when
C.how ; how
D.why ; why 此题选c,为什么不选d,这句话如何翻译?

why不能选是因为她既然去看医生,必然不知道自己的手是“为什么”开始颤抖的,后面一个空我觉得倒是两者都可以填.
翻译：老妇人的手经常颤抖.她向医生解释了半年前她的手势如何开始颤抖的,而且她又是如何仅仅因为手抖而不得不放弃了她的工作.