Meaning: 'Rather' means 'to a certain extent' or 'instead,' suggesting a preference for discussing life length rather than quality.

Wrong options:

• prefer: The word 'prefer' is a verb that indicates a choice, which does not fit grammatically in this context where an adverb is needed.
• better: 'Better' is a comparative adjective that implies superiority, but it does not grammatically fit as it does not serve the intended contrast in this sentence.
• quite: 'Quite' is an adverb that indicates degree but does not provide the necessary contrast between length and quality.

Correct answer: progress

Explanation: The term 'progress' fits contextually as it refers to advancements in health and quality of life, aligning with the discussion of life expectancy. It is a noun that appropriately describes the area being measured.

Meaning: 'Progress' refers to forward or onward movement towards a destination or goal, in this case, improvements in health metrics.

Wrong options:

• density: 'Density' refers to the degree of compactness of a substance, which does not relate to health or life expectancy.
• volume: 'Volume' refers to the amount of space an object occupies, which is irrelevant in this context of health indicators.
• surface: 'Surface' refers to the outermost layer or aspect of something, which does not convey the intended meaning related to health advancements.

Correct answer: while

Explanation: The word 'while' serves as a conjunction that introduces a contrast between the life expectancy of girls and boys, fitting grammatically and contextually within the sentence structure.

Meaning: 'While' means 'during the time that' or 'although,' indicating a contrast between the two subjects being discussed.

Wrong options:

• as: The word 'as' is used to indicate a role or function, which does not fit the contrasting context required here.
• which: 'Which' is a relative pronoun that introduces additional information but does not create the necessary contrast in this sentence.
• that: 'That' is also a relative pronoun used for defining clauses, but it does not convey the contrast needed in this context.

Correct answer: slightly

Explanation: The adverb 'slightly' indicates a small degree of change, fitting grammatically and contextually as it describes the increase in life expectancy for boys compared to girls.

Meaning: 'Slightly' means 'to a small extent' or 'a little,' indicating that the increase was not significant but still present.

Wrong options:

• lightly: 'Lightly' refers to something done with little weight or force, which does not convey the intended meaning of a small increase in life expectancy.
• dramatically: 'Dramatically' implies a significant or striking change, which contradicts the context of a small increase indicated by 'slightly.'
• slowly: 'Slowly' refers to the speed of change, which does not accurately describe the degree of increase in life expectancy.

Correct answer: in

Explanation: The preposition 'in' is used to indicate a state or condition, fitting grammatically and contextually as it describes the occurrence of increases within the timeframe of life expectancy.

Meaning: 'In' indicates a position or state within a certain context, here referring to the increases occurring during the specified time period.

Wrong options:

• at: 'At' is used to indicate a specific point or location, which does not fit the context of describing occurrences over a period of time.
• under: 'Under' implies being beneath or subject to something, which does not convey the intended meaning of increases happening during a time frame.
• for: 'For' indicates a purpose or duration, but it does not accurately describe the occurrence of increases in life expectancy.

Correct answer: most

Explanation: The word 'most' is used as a determiner to indicate the majority of something, fitting grammatically and contextually as it describes the extent of the 20th century during which life expectancy increased.

Meaning: 'Most' refers to the greatest amount or number, indicating that life expectancy increases occurred during the majority of the century.

Wrong options:

• the most: 'The most' is a superlative form that implies the highest degree, which does not fit the context of describing a general timeframe.
• a majority: 'A majority' is a noun phrase that does not fit grammatically in this context where a determiner is needed.
• a few: 'A few' indicates a small number, which contradicts the context of increases occurring during the majority of the century.