The correct answer is D. decorum.
"Decorum" refers to behavior in keeping with good taste and propriety, which is relevant in a courtroom setting. The other options do not fit the context as well:
A. umbrage - taking offense or annoyance. B. succor - assistance and support in times of hardship and distress. C. veracity - conformity to facts; accuracy.
Thus, the sentence would read: "Before the verdict was read, the judge warned the courtroom spectators to maintain proper decorum."