Dear student,
A) - Duodenum and jejunum of the stomach are the main absorptive site of digested food. The digested food contains the monomer forms of carbohydrates, proteins and fats and various minerals which gets absorbed by the enterocytes of duodenum and jejunum.
B) - Large intestine is the site of water absorption where undigested food is present. The absorption of water is via aquaporins.
Regards.