Topic: Sequence of Tense,

Best Answer Explained in Below-:

The correct option to complete the sentence "No sooner had the thief seen the policemen---" is **C) than he ran away**. This choice is appropriate because it follows the grammatical structure of a common English expression. The phrase "no sooner... than..." is an idiomatic construction that indicates an immediate sequence of events, implying that one action occurs right after another.

In this context, the thief seeing the policemen is the first event, and his running away is the second, which happens almost instantaneously. This construction emphasizes the quick reaction of the thief when confronted with a threat.

On the other hand, the other options do not fit this structure correctly. Option A suggests a temporal relationship with 'when' instead of 'than', which is incorrect in this context. Option B fails to convey the immediacy required, lacking the "no sooner... than" structure. Lastly, option D uses the past perfect tense incorrectly, as the thief's running away should be described as an immediate action following the sight of the policemen. Thus, C is the only option that correctly conveys the intended meaning.