Answer
Firstly, cellulose is not solely composed of carbon. Secondly, the structure of paper on a molecular level is not uniform and lattice, but rather random and messy.
Work Step by Step
The primary difference is the fact that the problem in both B and C are posed in a way that doesn't account for molecular imperfections in the structure. Cellulose is not JUST carbon, it also contains hydrogen and oxygen. Paper appears uniform and even on a macro scale, but on a microscopic level it's laden in messy and uneven fibers.
