A.I. Explanation:

Correct answer: how

Explanation: The word 'how' serves as an interrogative adverb that introduces the manner in which birth and death rates stabilize. It fits grammatically as it connects the explanation of the demographic transition model to the process described.

Meaning: 'How' is used to inquire about the manner or method of something, in this case, the stabilization of birth and death rates.

Wrong options:

• when: The word 'when' is a temporal adverb that refers to time, which does not fit the context of explaining the process of stabilization.
• thus: 'Thus' is an adverb that indicates a conclusion or result, which does not appropriately introduce the explanation of the process.
• rest: 'Rest' is a noun that refers to remaining parts, which does not fit grammatically or contextually in this sentence.
• stare: 'Stare' is a verb that means to look fixedly, which is irrelevant to the context of demographic changes.
• too: 'Too' is an adverb that indicates excessiveness, which does not fit the context of explaining how rates stabilize.

Correct answer: thus

Explanation: The word 'thus' is used as a conjunctive adverb that indicates a result or consequence. It fits contextually as it connects the idea of development to the outcome of discarding the previous theory.

Meaning: 'Thus' means 'as a result' or 'therefore,' indicating a logical connection between the development of a nation and the discarding of the theory.

Wrong options:

• when: 'When' is a temporal adverb that does not convey the causal relationship needed in this context.
• how: 'How' is an interrogative adverb that does not fit as it does not indicate a result or conclusion.
• rest: 'Rest' is a noun that does not fit grammatically or contextually in this sentence.
• stare: 'Stare' is a verb that is irrelevant to the context of demographic changes and does not fit.
• too: 'Too' is an adverb indicating excessiveness, which does not logically connect the ideas presented.

Correct answer: too

Explanation: The word 'too' is an adverb that indicates an excessive degree. It fits grammatically and contextually as it describes the theory of overpopulation in a negative light, suggesting that the world would become excessively populated.

Meaning: 'Too' means 'excessively' or 'more than is desirable,' indicating a negative connotation regarding population growth.

Wrong options:

• when: 'When' is a temporal adverb that does not fit the context of describing the state of overpopulation.
• how: 'How' is an interrogative adverb that does not describe the state of being overpopulated.
• thus: 'Thus' is a conjunctive adverb that indicates a result, which does not fit in describing the state of overpopulation.
• rest: 'Rest' is a noun that does not fit grammatically or contextually in this sentence.
• stare: 'Stare' is a verb that is irrelevant to the context of demographic changes and does not fit.