The answer is letter C. Modern Irish folk dance costumes are based on peasant garb. Although we are in the modern world, the modern Irish folk dance costumes are still based on the traditional Irish peasant dress which reflects the Irish clothing back in the eight century.
There have been many changes on the Irish folk dance costume, among of which is the footwear and stockings that women can wear – they are now wearing white socks since black stockings were already forbidden by the Church for being too seductive. These costumes are adorned with Celtic designs which are based on the Irish stone crosses and the Book of Kells. Of course, colors on the costume would always be present so as to highlight all the design.