Question

They ____ on the program for almost one week before I joined them

They ______ on the program for almost one week before I joined them, and now we _____on it as no good results have come out so far.
A. had been working; are still working B. had worked; were still working
C. have been working; have worked D. have worked; are still working
答案是C，为什么？

Answer 1

答案错了。应该是A，before i joined them,过去的过去，用过去完成时（过去完成进行时），因为一直未完成，还在持续，所以是过去完成进行时。“我们到目前没得出结果”说明我们还在一直工作

Answer 2

答案不对，应该选A
首句，before I joined them用的是一般过去时，那么before之前的动作是发生在过去的过去，应该用过去完成时，排除CD
次句中有明确的时间状语now，不会是B选项
故选A