The answer is motif :) any reoccurring theme, pattern, idea, image etc. in a work applies to this.
for example, an artist that includes flowers in across all of their work (or a series of it) would be depicting a floral motif. I hope this helps!!
My best guess is c( so yeahhh)
What era are you looking for? I know that many of the people used animal bones to carbe things. Or used paints made from plants
