Given:

A says: "Yes, B is a truth-teller."
B says: "No, I am not a truth-teller."
C says: "B is a liar."

We need to determine: Who is telling the truth?

Step 1: Assume B is a truth-teller:

If **B is a truth-teller**, then B's statement "No, I am not a truth-teller" would be false, which is a contradiction because a truth-teller cannot lie.

So, **B cannot be a truth-teller**.

Step 2: Assume B is a liar:

If **B is a liar**, then B's statement "No, I am not a truth-teller" must be false, meaning B is indeed a truth-teller. But this is a contradiction because B can't be both a liar and a truth-teller.

Thus, **B must be a liar**.

Step 3: A’s statement analysis:

A says, "Yes, B is a truth-teller." Since we concluded that **B is a liar**, A's statement is false.

This means **A is a liar**.

Step 4: C’s statement analysis:

C says, "B is a liar." Since **B is indeed a liar**, C’s statement is true.

Therefore, **C is a truth-teller**.

✅ Final Answer: C is the truth-teller.