Why are polysaccharides more difficult to digest than monosaccharides?

Polysaccharides are the complex carbohydrates that are formed by many units of simple sugar, which is also called monosaccharide.

They are large organic molecules having large number of glycosidic bond (formed between two simple sugar molecules) and therefore large amount of energy is required to break/digest them.

Moreover, they can not be absorbed in this form through gastrointestinal tract.

On the contrary, monosaccharide (simple sugar such as glucose) can be readily absorbed through gastrointestinal tract.

Thus, polysaccharides are more difficult to digest as compared to monosaccharides.

the answer to your question is:

c. complementary base-pairing