Like the rest of Chennai, our apartment has a water crisis. When the Secretary…

Subordinating conjunctions of time — such as before, after, until, and since — join two clauses by showing the order in which their actions occur. ‘Before’ introduces the clause whose action must happen first, so ‘A before B’ means A’s timing precedes B: the action in the ‘before’ clause is completed earlier than the action in the main clause.

In the third sentence, the main clause ‘The contractor needed the approval of the executive committee’ states a prerequisite, and the blank must connect it to ‘he could start installing another bore well.’ Approval has to be secured first, and only afterward can the work begin — exactly the sequence ‘before’ expresses: ‘The contractor needed the approval of the executive committee before he could start installing another bore well.’

• ‘after’ reverses the order of events — it would mean the contractor started the installation first and the committee’s approval followed later, which does not match the passage.

• ‘again’ is an adverb of repetition, not a conjunction that can join two clauses, and there is no earlier identical approval event here for it to refer back to.

• ‘because’ is a causal conjunction (it gives a reason), but the blank is not explaining why approval was needed — it is linking two events in a time sequence, which ‘because’ does not express.

Only ‘before’ matches both the required part of speech (a conjunction linking two clauses) and the sequence of events described, confirming it as the correct choice for the third blank.