Final answer:
The pylorus is the area of the stomach that adjoins the small intestine, specifically the duodenum, and is regulated by the pyloric sphincter.
Step-by-step explanation:
The area of the stomach that directly adjoins the small intestine is the pylorus. The pylorus connects the stomach to the duodenum, which is the first part of the small intestine. This connection is regulated by the pyloric sphincter, a ring of smooth muscle that controls stomach emptying. The pylorus can be subdivided into two regions: the wider pyloric antrum that connects to the body of the stomach and the narrower pyloric canal that connects to the duodenum. Therefore, the correct answer to the initial question is B. pylorus.