Select the most appropriate option to fill in the blank.
"At the sight of the police, the thief ran away in the ________ of an eye."

Explanation of the Correct Answer:
· The phrase "in the blink of an eye" means "very quickly, almost instantly."
· The correct word to complete the idiom is "blink."
Example Sentences:
· The magician disappeared in the blink of an eye.
· Opportunities can pass in the blink of an eye if you're not careful.
Other options:
· (a) "back" → Incorrect because "in the back of an eye" is not a valid phrase.
· (b) "sparkling" → Incorrect because "sparkling of an eye" does not make sense.
· (c) "core" → Incorrect because "core of an eye" is not an idiomatic phrase.
Thus, the correct answer is (d) "blink."