Which of the following tissues normally has the highest percentage of mucus-secreting cells?

Salivary glands can contain predominantly serous cells, predominantly mucous cells, or both in their acini. As you proceed from the midline laterally, acini in the sublingual gland are almost pure mucous cells, while acini in the submandibular gland contain a mixture of serous and mucous cells. Acini in the parotid gland are mostly pure serous cells. The esophageal mucosa and the oral mucosa are squamous epithelia that do not form acini. Ref: Color Atlas of Cytology, Histology, and Microscopic Anatomy by Wolfgang Kuhnel