Meaning: 'According' means 'as stated by' or 'in agreement with,' indicating that the information that follows is based on the referenced study.

Wrong options:

• resorting: 'Resorting' implies turning to something for help or support, which does not fit the context of referencing a study.
• coursing: 'Coursing' refers to the act of running or flowing, which is unrelated to the context of citing research findings.
• assorting: 'Assorting' means categorizing or grouping, which does not align with the grammatical structure needed to introduce a study.

Correct answer: bothered

Explanation: The word 'bothered' is appropriate here as it conveys a sense of concern or unease regarding the situation described. It fits grammatically and contextually, as the scientists are expressing their feelings about the paradox of increased wealth and stagnant happiness.

Meaning: 'Bothered' means feeling troubled or concerned about something, indicating the scientists' emotional response to their findings.

Wrong options:

• disentangled: 'Disentangled' means to free from entanglement, which does not fit the emotional context of concern expressed by the scientists.
• adapted: 'Adapted' implies making changes to fit a new situation, which does not convey the scientists' feelings about their observations.
• charted: 'Charted' means to map out or plan, which does not align with the emotional response needed in this context.

Correct answer: flatlined

Explanation: The term 'flatlined' is used here to indicate that happiness levels have remained constant or unchanged over time, fitting both grammatically and contextually within the sentence.

Meaning: 'Flatlined' means to remain at a stable level without any increase or decrease, often used in medical contexts but here applied to happiness levels.

Wrong options:

• capsized: 'Capsized' means to overturn or flip over, which does not relate to the concept of happiness levels remaining unchanged.
• umpired: 'Umpired' refers to officiating a game, which is irrelevant to the context of happiness levels.
• trioxide: 'Trioxide' is a chemical term and does not fit the context of discussing happiness.

Correct answer: rate

Explanation: The word 'rate' is suitable here as it refers to the act of assessing or evaluating happiness, fitting grammatically and contextually with the action the scientists are asking the volunteers to perform.

Meaning: 'Rate' means to evaluate or assess the level of something, in this case, the participants' happiness.

Wrong options:

• render: 'Render' means to provide or give, which does not fit the context of assessing happiness levels.
• lend: 'Lend' implies giving temporarily, which does not align with the action of evaluating happiness.
• ramp: 'Ramp' refers to a slope or incline, which is unrelated to the context of measuring happiness.

Correct answer: participants

Explanation: The term 'participants' is the correct choice as it refers to individuals taking part in the study, fitting grammatically and contextually within the sentence.

Meaning: 'Participants' means individuals who take part in an activity or study, in this case, the volunteers in the happiness experiment.

Wrong options:

• filaments: 'Filaments' refers to thin threads or fibers, which does not relate to people involved in a study.
• nonbelligerents: 'Nonbelligerents' refers to those not engaged in conflict, which is irrelevant to the context of a study about happiness.
• thimblefuls: 'Thimblefuls' refers to small amounts, typically of liquid, which does not fit the context of individuals participating in research.