Step 1: Concept
In conditional or time clauses introduced by words like "until," "if," or "when," we use the simple present tense to refer to the future, not the future tense ("will").
Step 2: Meaning
The speaker is expressing a future intention dependent on the bus stopping.
Step 3: Analysis
Part 4 uses "will stop," which is incorrect after the time conjunction "until". It should be "it stops".
Step 4: Conclusion
The mistake is in Part 4.
Final Answer: (D)