His frivolous remarks provoked no comments.

Answer: Option A

Frivolous : not having any serious purpose or value.
Serious : demanding or characterized by careful consideration or application.
Momentous : of great importance or significance, especially in having a bearing on future events.
Frantic : distraught with fear, anxiety, or other emotion.
Fanciful : over-imaginative and unrealistic.

Antonym of Frivolous is Serious