In the following sentence, the bracketed part is incorrect. Choose the option that best improves the bracketed part so that the sentence is grammatically correct. He jumped off the train while it (had been running).

Introduction / Context:
This sentence improvement question examines your understanding of the correct tense and aspect to describe two actions happening at the same time in the past. The sentence talks about a person jumping off a train at the time when the train was in motion. The bracketed phrase uses an incorrect tense, and you must select the option that gives a natural and grammatically correct expression of this simultaneous action.

Given Data / Assumptions:
- Original sentence: He jumped off the train while it (had been running). - Options: has been running, ran, was running, No improvement. - The jump is a completed action in the past, and the train was in motion at that time.

Concept / Approach:
When one action happens in the middle of another continuous action in the past, English generally uses the simple past for the shorter action and the past continuous for the longer background action. Here, the short action is he jumped, and the ongoing background action is the train moving. Therefore, the correct structure is while it was running. The past perfect continuous had been running suggests a state that was already finished before another past reference point, which does not match the idea of the train running at the moment of the jump.

Step-by-Step Solution:
Step 1: Identify actions and timing. The jump happened at a specific moment, and the train's running is the ongoing background event. Step 2: Apply the rule: simple past for the shorter, interrupting action (jumped) and past continuous for the longer action in progress (was running). Step 3: Test was running. He jumped off the train while it was running sounds natural and correctly describes the situation. Step 4: Test had been running. He jumped off the train while it had been running suggests that the train's running had already ceased before the jump, which is illogical. Step 5: Test ran. He jumped off the train while it ran is grammatically possible but not idiomatic; native speakers normally say while it was running. Step 6: No improvement cannot be correct because had been running is clearly an inappropriate tense here.

Verification / Alternative check:
Compare with similar, familiar structures. We say He broke his leg while he was playing football and She called me while I was driving. Replacing was playing or was driving with had been playing or had been driving would change the meaning to something that had finished before the incident. In the same way, while it was running fits the pattern, while it had been running distorts the sequence of events. This comparison confirms that was running is the correct choice.

Why Other Options Are Wrong:
Has been running is wrong because it is present perfect continuous, which connects the action to the present, while the entire sentence is clearly about a completed past event. Ran is wrong because, although it is past tense, it does not emphasise the ongoing nature of the action during the jump and sounds less natural than was running. No improvement is wrong because the original phrase had been running misrepresents the timing and is not how native speakers describe this situation.

Common Pitfalls:
Learners often overuse the past perfect and past perfect continuous because they seem more complex and therefore more suitable for exams. However, these tenses are only appropriate when you need to show that one past action was completed before another past reference point. When two actions happen simultaneously, with one acting as background, the simple past plus past continuous pattern is usually correct. Remembering this pattern will help you in many sentence improvement questions similar to this one.

Final Answer:
The correct improvement is: He jumped off the train while it was running.