A.I. Explanation:

Correct answer: within

Explanation: The word 'within' indicates a time frame that is inclusive of the past 12,000 years, fitting grammatically and contextually as it suggests that the transition occurred during this period.

Meaning: 'Within' means 'inside the limits of' or 'during the time period of,' indicating that the events happened during the last 12,000 years.

Wrong options:

• before: The word 'before' implies a time prior to a certain point, which does not fit the context of the transition occurring during the past 12,000 years.
• by: The word 'by' suggests a deadline or limit, which does not accurately convey the ongoing nature of the transition within the specified time frame.
• since: The word 'since' indicates a starting point in the past continuing to the present, which does not align with the specific time frame of the last 12,000 years.

Correct answer: could control

Explanation: The phrase 'could control' indicates ability in the past, fitting grammatically as it aligns with the past tense context of the sentence, suggesting that humans had the capability to manage growth and breeding.

Meaning: 'Could control' means having the ability to manage or influence something, in this case, the growth and breeding of plants and animals.

Wrong options:

• controlled: The word 'controlled' is in the past tense and suggests a completed action, which does not fit the context of expressing ability at that time.
• were controlling: The phrase 'were controlling' implies an ongoing action in the past, which does not convey the intended meaning of ability at that time.
• would control: The phrase 'would control' suggests a future possibility or intention, which does not fit the past context of the sentence.

Correct answer: led to

Explanation: The phrase 'led to' indicates a cause-and-effect relationship, fitting grammatically and contextually as it shows that the discovery resulted in farming and herding.

Meaning: 'Led to' means to cause something to happen or to result in, indicating that the discovery was a catalyst for farming and herding.

Wrong options:

• carried on: The phrase 'carried on' suggests continuation rather than a result, which does not fit the context of the discovery causing farming and herding.
• made: The word 'made' is too vague and does not convey the specific causal relationship implied in the sentence.
• resulted from: The phrase 'resulted from' indicates a consequence rather than a cause, which is the opposite of what is intended in this context.

Correct answer: As

Explanation: The word 'As' indicates simultaneous actions, fitting grammatically and contextually as it shows that the investment of time in food production occurred concurrently with settling down.

Meaning: 'As' means 'at the same time that,' indicating that the actions of investing time and settling down happened together.

Wrong options:

• if: The word 'if' introduces a conditional clause, which does not fit the context of describing simultaneous actions.
• so: The word 'so' implies a consequence or result, which does not accurately convey the relationship between the two actions in this context.
• With: The word 'With' suggests accompaniment but does not effectively indicate the simultaneous nature of the actions as 'As' does.

Correct answer: that

Explanation: The word 'that' introduces a clause explaining the extent of success, fitting grammatically and contextually as it connects the success of the species to the creation of a turning point.

Meaning: 'That' is used to introduce a defining clause, indicating the reason or explanation for the success of the species.

Wrong options:

• but: The word 'but' introduces a contrast, which does not fit the context of explaining the success of the species.
• though: The word 'though' also introduces a contrast or concession, which is not appropriate in this context.
• which: The word 'which' is used to provide additional information but does not effectively connect the success to the turning point as 'that' does.