Meaning: 'Again' means 'once more' or 'another time,' indicating the cyclical nature of the refrigerant's state changes.

Wrong options:

• yet: 'Yet' suggests something that has not happened up to this point, which does not fit the context of a repeated process.
• aside: 'Aside' means 'to one side' or 'out of the way,' which does not relate to the process of changing states in this context.
• around: 'Around' implies a circular movement or location, which does not accurately describe the process of changing states.

Correct answer: produce

Explanation: The verb 'produce' is appropriate here as it indicates the generation of energy, which is a key function of heat pumps. It fits grammatically and contextually, as the sentence discusses the energy output of the system.

Meaning: 'Produce' means 'to create or generate,' referring to the heat pump's ability to generate more energy than it consumes.

Wrong options:

• imitate: 'Imitate' means to copy or mimic, which does not apply to the process of generating energy in this context.
• deplete: 'Deplete' means to reduce or use up, which is the opposite of what heat pumps do in terms of energy generation.
• conceal: 'Conceal' means to hide or keep something out of sight, which is irrelevant to the function of producing energy.

Correct answer: target

Explanation: The word 'target' is suitable as it refers to a specific goal or objective, which aligns with the context of the UK aiming for net zero emissions. It fits grammatically and contextually as a noun describing the goal.

Meaning: 'Target' means a goal or aim that one strives to achieve, in this case, the emissions goal set by the UK.

Wrong options:

• term: 'Term' refers to a word or expression, which does not convey the idea of a goal in this context.
• boundary: 'Boundary' implies a limit or edge, which does not fit the context of a goal or aim.
• trend: 'Trend' refers to a general direction in which something is developing, which does not accurately describe a specific goal.

Correct answer: relatively

Explanation: The adverb 'relatively' is appropriate as it indicates a comparison, suggesting that heat pumps are uncommon compared to other heating systems. It fits grammatically and contextually within the sentence structure.

Meaning: 'Relatively' means 'in relation or comparison to something else,' indicating that heat pumps are uncommon when compared to other heating solutions.

Wrong options:

• precisely: 'Precisely' means exactly or accurately, which does not convey the comparative nature needed in this context.
• abruptly: 'Abruptly' means suddenly or unexpectedly, which does not fit the context of describing the commonality of heat pumps.
• regularly: 'Regularly' means occurring at fixed intervals, which does not accurately describe the uncommon status of heat pumps.

Correct answer: announced

Explanation: The verb 'announced' is fitting as it indicates that the government has made a public declaration regarding the increase in grants. It fits grammatically and contextually as it describes an action taken by the government.

Meaning: 'Announced' means to make a public statement about something, in this case, the increase in boiler upgrade grants.

Wrong options:

• underestimated: 'Underestimated' means to assess something as less than its actual value, which does not fit the context of making a declaration.
• diverted: 'Diverted' means to change the direction of something, which does not apply to the context of announcing a grant increase.
• told: 'Told' is a more informal way of saying to inform someone, but it lacks the formal context needed for a government announcement.