Lymphoid tissue that appears as a swelling of the mucosa in the oral cavity is called a(n) .

There are choices for this question namely: 

A) tonsil
B) thymus
C) Peyer's patch
D) appendix

The correct answer is "tonsil". Tonsils are lymphoid tissue that is found in the oral mucosa. The tonsils are arranged in a ring-like fashion called the Waldeyer's ring. This ring comprises of two tubal tonsils, two palatine tonsils, one adenoid tonsil, and one lingual tonsils. In cases of infection involving the oral mucosa and the pharynx, the tonsils become inflamed as well and the condition is called acute tonsillopharyngitis.

The correct answer is a. we know this because n (hap) + n (hap) = 2n (dip).