The transverse section of the human alimentary canal consists of 4 distinct layers. 1. the innermost mucosa, 2. submuosa on top of the mucosal layer, 3. Muscularis- a layer of smooth muscles covering the submucosal layer. 4. serosa- the outermost layer of the alimentary canal.
In the figure, the A - represents the innermost layer mucosa and B the layer on top of mucosa called the submucosa. Thus, the correct option is A.