Why Does a Starchy Food, Like Bread, Become Hard and Stale

Why does a starchy food, like bread, become hard and stale when it dries out?

A) Cellulose molecules aggregate in the absence of water.
B) In the absence of water, unbranched starch forms hydrogen bonds between polysaccharides, which then aggregate.
C) The release of carbon dioxide causes the bread to harden.
D) Water and heat cause the polysaccharide chains to bind together.
E) Mold growth interferes with $\alpha$ linkages, causing the bread to harden.