Which of the following sentences correctly contains a relative pronoun introducing a relative clause?

Introduction / Context:
This question checks whether you can recognise a relative pronoun and the relative clause it introduces. Relative pronouns such as who, whom, whose, which, and that are very important for joining ideas and adding extra information about a noun. Many questions on clause structure and sentence improvement depend on these concepts.

Given Data / Assumptions:
- We must select the sentence that actually uses a relative pronoun.
- A relative pronoun introduces a clause that describes a noun, often called an adjective or relative clause.
- The options contain words like that and whom, but not all of them are used as relative pronouns.

Concept / Approach:
A relative pronoun typically comes just after the noun it describes and starts a clause that gives more information about that noun, for example "The man who lives next door" or "The book that I bought yesterday". In the correct structure, if you remove the relative clause, the main sentence still makes sense, but with less information. In this question, we must look for such a pattern.

Step-by-Step Solution:
Step 1: Examine option c: "The girl whom you met yesterday is my sister."
Step 2: Identify the noun "The girl" and the clause "whom you met yesterday". The word "whom" introduces the clause and refers back to "girl".
Step 3: Check whether removing the relative clause gives a complete sentence: "The girl is my sister" is still meaningful, so "whom you met yesterday" is additional information.
Step 4: Conclude that "whom" is a relative pronoun here and option c is the correct choice.

Verification / Alternative check:
Look at the other options. In "That is my book bag", the word "That" is a demonstrative pronoun pointing to an object, not a relative pronoun introducing a clause. "Some boys are coming for tuition" and "My cousin lives in Delhi" have no relative clauses at all. "Those are not your things" also uses "Those" as a demonstrative pronoun, not as a relative pronoun. Therefore, only option c fits the definition given in the question.

Why Other Options Are Wrong:
- That is my book bag: "That" simply points to an object; it does not start a describing clause.
- Some boys are coming for tuition: there is only one clause and no relative pronoun.

- Those are not your things: again, "Those" is demonstrative, not relative.
- My cousin lives in Delhi: simple sentence with no relative clause.

Common Pitfalls:
Students often think that any sentence with the word "that" contains a relative pronoun. However, "that" can function as a demonstrative, complementiser, or relative pronoun, depending on its position and role. A good test is to see whether the word starts a clause that gives extra information about a noun, and whether the clause can be removed while leaving a complete core sentence.

Final Answer:
The correct sentence with a relative pronoun is "The girl whom you met yesterday is my sister."