In the assigned reading "The fashioning of women", the authors discuss the String Revolution. Which of the following is considered a certainty about fibre artifacts, as discussed by them?

a$.$ Fibre artifacts are highly perishable.

b$.$ If found with stone artifacts, fibre artifacts outnumber stone artifacts $20$:$1.$

c$.$ The method by which the fibre artifact was made is evident on the artifact itself.

d$.$ All of the above are certainties about fibre artifacts.