There haven't been the needed/necessary signs of improvement for us to remain hopeful.
Does this read natural?
" That keeps "needed/necessary" together with its preposition "for".
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Is is normal everyday English, and I think that many native speakers would put it that way off the cuff, but I think it would be better as "There haven't been the signs of improvement needed/necessary for us to remain hopeful." That keeps "needed/necessary" together with its preposition "for".