Why is folding and three-dimensional shape of molecules so important in biology?

The correct answer is option A, that is, denatures.  

The extreme temperatures lead to the unfolding of a polypeptide chain resulting in a change in composition and generally a loss of function. If the protein working as an enzyme denatures, it will make that protein to lose its enzymatic activity.  

As the temperature of a solution comprising the protein is elevated, the extra heat results in bending and twisting of bonds. As proteins start to denature, the secondary composition of the protein is lost and adopts a random coil configuration. The covalent association among the amino acid side chains like disulfide bonds also gets lost.