Select whichever preposition or determiner you consider the most appropriate for the blank space.
We had a discussion __________ the project.

Correct option is C

The word that can be filled in the blank is ‘about’ to make the sentence grammatically and contextually correct.
• ‘About’ is used to indicate discussion on a particular topic.
• As per the context, the word ‘about’ fits very well & hence, it is the correct option.
Meanings of other given words:
• Beneath - used to indicate something physically lower than something else.
• With - used to indicate accompanied by another person or thing.
• In - used to indicate inclusion within space, a place, or limits.
• Thus, all the other given words have different meanings and do not fit in the context of the sentence.