The correct answer is D. impropriety.
A scandal is an action or event regarded as morally or legally wrong and causing general public outrage. In this case, the murderer was declared innocent, which is considered to be an impropriety because it is morally wrong to let a murderer go free.
A rumour is a piece of unverified information that is spread from person to person. In this case, the rumour could be that the murderer was declared innocent because they were rich or had connections.
Silly is an adjective that means foolish or stupid. In this case, it would be silly to say that the murderer was declared innocent because they were rich or had connections.
Talk is a verb that means to speak about something. In this case, it would be talk to say that the murderer was declared innocent because they were rich or had connections.
I hope this helps!