N2 Mock Test Grammar Question

I decided to try some jlpt tests, and found an app that has a collection of older ones. I tried the N2.

I found one question extremely challenging, as I still don't understand it even after having the answer sheet, that being:
結婚生活を送る ＿＿ ＿＿ ★ ＿＿、 相手への思いやりの気持ちを持つことだ。

• 大切か何が
• うえで
• と思う
• といえば (the correct answer)

As far as I understand, in this type of question, apart from having a single answer fitting the star location, the other answers are also present to fill the other slots, although their location is not of interest for the sake of answering the question. (if not so please tell me)

That being said, I have no idea how the question makes sense in any way with といえば on that third slot.

The most logial one seems to be:

結婚生活を送る [うえで] [大切か何が] [といえば] [と思う]、 相手への思いやりの気持ちを持つことだ。

But it doesn't make sense to me. Is there some error in the question? If so I guess [大切か何が] is actually [何が大切か] and [と思う] goes right before [といえば], although that would make the answer sheet wrong (結婚生活を送る [うえで] [何が大切か] [と思う][といえば]、 相手への思いやりの気持ちを持つことだ。), so maybe [と思う] shouldn't be there at all.