Here is the Venn diagram you requested, illustrating that the union of sets $A$ and $B$ is entirely contained within set $C$. Let me know if you'd like further clarification or modifications.

Would you like additional details or have any questions?

Here are 5 related questions to expand on the topic:

1. What does it mean if $A \cap B \subseteq C$?
2. How would the Venn diagram change if $A \cup B \not\subseteq C$?
3. Can you provide an example of specific sets where $A \cup B \subseteq C$?
4. How can $A \cup B = C$ be represented in a Venn diagram?
5. What is the significance of subsets in set theory?

Tip: Always verify relationships in set theory using definitions of union ($\cup$), intersection ($\cap$), and subsets ($\subseteq$) to avoid misinterpretations.