The correct answer is C. abusive.
Scurrilous means “offensively coarse or vulgar in language or behavior.” In the context of the question, some of the members of the Board indulged in highly scurrilous talk at the meeting, meaning that they used offensive or vulgar language. This is considered to be abusive behavior, as it is likely to cause offense or harm to others.
The other options are incorrect because they do not accurately describe the behavior of the Board members. Option A, irrelevant, is incorrect because the Board members’ talk was not irrelevant to the meeting. Option B, superfluous, is incorrect because the Board members’ talk was not unnecessary or excessive. Option D, objectionable, is incorrect because the Board members’ talk was not simply objectionable, but was also abusive.