In which sentence is a homophone used correctly

if the italicized noun phrase is "the chairman", the correct option is s (subject). this noun phrase performs the syntactic function of subject of the main clause, as it preceeds the verb phrase ("heard") and is the doer of the action.

if the italicized noun phrase is "what was said about the program", the correct option is do (direct object). this noun phrase follows a transitive verb ("heard"), which requires a direct object to fully complete its meaning.

if the italicized noun phrase is "the program". the correct option is op (object of preposition). this noun phrase follows a preposition ("about"), which requires a prepositional object in order to complete its meaning.