Why is cellulose so difficult for most animals to digest?

A) they don't have the proper enzyme to break the bonds between subunits

B) cellulose is made up of chitin, which is indigestible

C) the bonds holding cellulose subunits together are extremely strong, stronger than in any other macromolecule

D) there are many hydrogen bonds holding the subunits together

The answer is C. Cellulose is a long chain of glucose and to be able to use any of the energy stored in them an organism must break it down into single glucose molecules, and this is why most animals go for a different diet. The chain is very difficult to break down and must be treated with concentrated acids at high temperature. This is a hard task to do and often time needs many stomachs.