In each of the questions given below, a statement with a highlighted phrase is given. Choose the most appropriate replacement from the given options which could replace the highlighted phrase to make the statements grammatically and contextually correct. If the highlighted phrase is already correct then choose option “No replacement required” as your response.

The police came after the thief run away.

The correct answer is had run away.

Step-by-step Explanation:

1. Analyze the Sentence Structure and Sequence of Events:
The given sentence is: "The police came after the thief run away."
This sentence describes two actions that took place in the past:
- Action 1: The thief running away.
- Action 2: The police coming.

2. Understand Past Perfect Tense Rules:
When two actions happened in the past, the action that occurred earlier or first must be expressed in the Past Perfect Tense ($\text{had}+{\text{V}}_3$ form of the verb). The action that happened later is expressed in the Simple Past Tense (${\text{V}}_2$ form of the verb).

3. Apply the Rule to the Sentence:
- First action: The thief escaped (earlier past action) ⇒ requires Past Perfect Tense ("had run away").
- Second action: The police arrived (later past action) ⇒ expressed in Simple Past Tense ("came").

4. Evaluate the Highlighted Phrase:
"run away" is incorrect because "run" in this context lacks the auxiliary verb "had" needed to form the past perfect tense required after "after".

5. Conclusion:
Replacing "run away" with "had run away" makes the sentence grammatically and contextually correct: "The police came after the thief had run away."