问题补充:
Only in this way, directed by the teacher, work out the problem the day before.
A. had they
B. they could
C. could they
D. did they
答案:
A. had they
B. they could
C. could they
(答案→)D. did they
解析:考查倒装句。当only位于句首是,主句采用部分倒装,助动词提前。句意:只有按照老师指导的这种方法,前一天他们才能解决这个难题。结合语境可知本句描述的是过去的动作,故用一般过去时态。助动词用did,选D。