Mucin is not secreted by: (A) Goblet cell, (B) Paneth cell, (C) Brunner's gland, (D) Crypts of Lieberkuhn
Answer is B. Paneth cells are a specific type of cell within the crypts of Lieberkuhn.
These cells have atypically oriented bright eosinophilic granules containing a variety of antimicrobial proteins and play a role in mucosal immunity (and not mucin secretion)

Brunner's glands: are sub-mucosal mucus gland within the duodenum.
Goblet cells: are mucin-secreting cells.
Crypts of Lieberkuhn: are lined by goblet cells besides other cell types.

These are thus also involved in mucin secretion.