I think i got confused by these three words: eylu, eyzo, and be'eyzo... They have the same meaning. Are those words interchangeable?
Are these the shirts that she wants? - would be: אלה החולצות שהיא רוצה? The relative clause is marked by החולצות ש.
So איזו and אילו have the same meaning. We always can use the one when we use the other?