A.I. Explanation:

Correct answer: started

Explanation: The word 'started' is the simple past tense of 'start,' which correctly indicates that the action of growing food occurred in the past. This fits grammatically as it aligns with the past context of the sentence, where early humans transitioned from hunter-gatherers to agricultural practices.

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.