Among all single bonds, only those involving hydrogen have signals in the functional group region of an infrared spectrum. What is the main reason behind this phenomenon?

a.) All X-H bonds (X=any element) are much stronger than any other single bond.

b.) Hydrogen has a much smaller atomic mass.

c.) All X-H bonds (X=any element) are much shorter than any other single bond.

d.) All X-H bonds (X=any element) are more polar than any other single bond.