The correct option is
A Unicellular mucous gland
Goblet cells are the modified simple epithelial columnar cells. It is found in the lining of organs like intestine and respiratory tract. It secretes mucin (glycoprotein) and maintains the layer of mucus. As each cell secretes mucin for mucous production it is called as a unicellular mucous gland.
So, the correct answer is 'Unicellular mucous gland'