Mucosa-associated lymphoid tissue (MALT) is located within the lining of -

Respiratory, digestive and urogenital tracts

The correct answer is Option (4) → Respiratory, digestive and urogenital tracts 

Lymphoid organs: These are the organs where origin and/or maturation and proliferation of lymphocytes occur. The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes.

There is lymphoid tissue also located within the lining of the major tracts (respiratory, digestive and urogenital tracts) called mucosa- associated lymphoid tissue (MALT). It constitutes about 50 per cent of the lymphoid tissue in human body.