The set of propositions
which was discussed by the panel have been published in the society journal.
Lets now break the sentence and read it once again.
Whats was discussed :- Prepositions -plural
What is published:- The Set (which comprised of prepositions)-singular
In option D- "which" is referring to Prepositions hence the use of "were" is apt.
The correct statement would look like :
The
set of
propositions which were discussed by the panel has been published in the society journal.
OA is correct.. It has to be D
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