The prevailing emotion or mood found in the excerpt is joyful. This is clear when we pay attention to the author's approach to the scene, apparently there has been battle and it is done now, and the speaker encourages people to forget it, perhaps because of the misery that comes with war, and instead he incites the audience to focus on singing, dancing all night long, and following Bacchus who led them to make Thebes shake, which are all signs that the author wants to evoke joyful and cheery feelings.
The word "dancing" indicates a positive mood of celebration, triumph and happiness. This pleasant mood is enhanced by the mention of Bacchus who is the god of agriculture and wine as well fertility, drama, and revelry. Hence, the best way to forget something negative like war is to celebrate with dancing and songs/music.
The word "dancing" means that they are happy and that they have reasons to celebrate, since a certain battle has ended. In this way, the word "dancing" conveys to the reader a mood of joy, happiness, satisfaction and celebration.
Seems like this question's answer choice is a mistake. The real answer is C. Melanchochy.
should be the answer.