I was shocked to hear the scurrilous talks of the members of the Board.

Answer: Option A

Scurrilous : making or spreading scandalous claims about someone with the intention of damaging their reputation.
Decent : conforming with generally accepted standards of respectable or moral behaviour.
Relevant : closely connected or appropriate to what is being done or considered.
Accurate : (especially of information, measurements, or predictions) correct in all details; exact.
Useful : able to be used for a practical purpose or in several ways.

Antonym of Scurrilous is Decent