Step 1: Understanding the Concept
The small intestine has three parts: duodenum, jejunum and ileum. The large intestine begins with the caecum.
Step 2: Junction
The ileum opens into the caecum through the ileocaecal valve.
Step 3: Compare the options
Duodenum-jejunum and jejunum-ileum are junctions inside the small intestine, and stomach-duodenum joins the stomach to the small intestine.
Final Answer:
The small intestine opens into the large intestine at the ileum and caecum.
\[ \boxed{\text{(C) }\text{ileum and caecum}} \]