Sometimes folding forces layers to: a. bend b. age c. melt d. harden

Sometimes folding forces layers to bend.

Explanation:

The layers underlying the Earth's surface are generally subjected to intense forces acting upon them from all the sides. These forces are usually the maximum when there is an occurrence of tectonic plate activity. During a tectonic plate activity, the layers are left with no room to move, and as a result, tectonic folding ends up in permanently deforming the layers by bending them.