Epithelial cells of the intestine involved in food absorption have on their surface

A patient is generally advised to specially consume more meat, lentils, milk and eggs in diet only when he suffers from

Which group of three of the following five statements (1 - 5) contain all three correct statements regarding beri-beri?
1.  A crippling disease prevalent among the native population of sub-Saharan Africa
2.  A deficiency disease caused by lack of thiamine (vitamin B₁)
3.  A nutritional disorder in infants and young children when the diet is persistently deficient in essential protein
4.  Occurs in those countries where the staple diet is polished rice
5.  The symptoms are pain from neuritis, paralysis, muscle wasting, progressive oedema, mental deterioration and finally heart failure.

The richest sources of vitamin B₁₂ are