$($c$)$ What two extraneous variables are mentioned in the problem description? $($Select all that apply.$)$

number of pages in the book

binding strength

paperback book or hardback book

types of glue

material of book

Can you think of any other extraneous variables that should be considered? $($Select all that apply.$)$

subject matter of the book

color of the book cover

dust jacket or no dust jacket

type of paper used

weight of material used in the cover