Meaning: 'Started' means to begin or commence an action, in this case, the action of growing food.

Wrong options:

• having started: This form is a perfect participle, which does not fit the past narrative of the sentence as it suggests an action completed before another past action, which is not the case here.
• starting: This gerund form does not fit grammatically as it cannot serve as the main verb in this context, which requires a past tense verb.
• start: This present tense form does not match the past context of the sentence, as it implies an ongoing action rather than a completed one.

Correct answer: so

Explanation: The word 'so' serves as a conjunction that indicates a consequence or result, linking the need for water to the establishment of settlements. It fits contextually as it shows the logical connection between the two clauses.

Meaning: 'So' means 'for that reason' or 'therefore,' indicating that settlements grew near water sources due to the necessity of water for crops and people.

Wrong options:

• because: This word introduces a reason rather than a consequence, which does not fit the intended meaning of the sentence that describes the result of needing water.
• thus: While 'thus' can indicate a conclusion, it is more formal and less commonly used in conversational contexts, making 'so' a better fit here.
• thereby: This word implies a means of achieving something, which does not align with the straightforward cause-and-effect relationship intended in the sentence.

Correct answer: long history

Explanation: The phrase 'long history' appropriately describes the extensive duration of water resource management, fitting grammatically as a noun phrase that serves as the subject complement in the sentence. It conveys the idea of a significant and established past.

Meaning: 'Long history' refers to a substantial period during which something has existed or been practiced, in this case, the management of water resources.

Wrong options:

• meticulous study: This phrase implies a careful examination, which does not accurately describe the concept of a historical timeline and lacks the necessary context of duration.
• moderate change: This phrase suggests a slight alteration, which does not fit the context of a historical account and does not convey the idea of a long-standing practice.
• brief existence: This phrase indicates a short duration, which contradicts the intended meaning of a well-established practice over time.

Correct answer: which

Explanation: The word 'which' is a relative pronoun that introduces a non-defining relative clause, providing additional information about the systems mentioned. It fits grammatically as it connects the clause to the noun it describes, enhancing the sentence's clarity.

Meaning: 'Which' is used to refer to a specific thing or things previously mentioned, in this case, the water supply and drainage systems.

Wrong options:

• as: This word is a conjunction that does not appropriately introduce a relative clause, making it unsuitable for connecting the ideas in this context.
• what: This word is an interrogative pronoun and does not fit grammatically as it does not serve to introduce additional information about the systems.
• whatever: This word implies a lack of specificity and does not function correctly as a relative pronoun in this context, failing to connect the clause meaningfully.