The Diary of Anne Frank tells the true story of a young girl and her family that were hidden during the Nazi occupation of the Netherlands by a gentile Dutch couple, though they were eventually discovered.
A) that were hidden during the Nazi occupation of the Netherlands by a gentile Dutch couple, though they were eventually discovered
B) that were hidden by a gentile Dutch couple during the Nazi occupation of the Netherlands, though they were eventually discovered
C) whom a gentile Dutch couple hid during the Nazi occupation of the Netherlands but were eventually discovered
D) who were hidden by a gentile Dutch couple during the Nazi occupation of the Netherlands but were eventually discovered
E) who were hidden by a gentile Dutch couple during the Nazi occupation of the Netherlands even though they were eventually discovered
I understand why a,b, and e are incorrect and I also understand why C doesn't make sense since whom makes the young girl and her family the object. However, I also am confused as to why D is correct since it is in in the passive voice. "young girl and her family were hidden by..." Why is this the correct answer? Why is D a better answer than C?