Meaning: 'Colossal' means extremely large or great, emphasizing the vast amount of effort needed to tackle climate change effectively.

Wrong options:

• nominal: 'Nominal' refers to something that is minimal or insignificant, which contradicts the context of needing a large effort.
• negligible: 'Negligible' means so small or unimportant that it can be disregarded, which does not match the context of the required effort being substantial.
• customary: 'Customary' refers to something that is usual or traditional, which does not convey the sense of urgency or scale needed in this context.

Correct answer: infrastructure

Explanation: The term 'infrastructure' is appropriate as it refers to the fundamental facilities and systems serving a country, city, or area, which are energy-intensive. This fits contextually with the discussion of energy use and development cycles.

Meaning: 'Infrastructure' means the basic physical and organizational structures needed for the operation of a society or enterprise, particularly in relation to energy consumption.

Wrong options:

• agriculture: 'Agriculture' pertains to farming and food production, which is not the focus of energy-intensive systems discussed in this context.
• architecture: 'Architecture' refers to the design and construction of buildings, which does not directly relate to the energy systems being discussed.
• conjecture: 'Conjecture' means an opinion or conclusion formed on the basis of incomplete information, which is irrelevant to the context of energy systems.

Correct answer: altering

Explanation: The word 'altering' is a gerund that fits grammatically and contextually, indicating a change to the energy system. It suggests a significant transformation is needed, which aligns with the overall message of urgency in addressing climate change.

Meaning: 'Altering' means making a change or modification, particularly to the energy system in this context.

Wrong options:

• revoking: 'Revoking' means to take back or withdraw, which does not fit the context of making changes to the energy system.
• comparing: 'Comparing' refers to evaluating similarities and differences, which is not relevant to the action of changing the energy system.
• analyzing: 'Analyzing' means examining in detail, which does not convey the action of making changes to the energy system.

Correct answer: curbing

Explanation: The word 'curbing' is a gerund that fits grammatically and contextually, indicating the action of limiting or controlling growth in emissions. It aligns with the need to manage emissions from coal effectively.

Meaning: 'Curbing' means to restrain or limit something, particularly in this context referring to the growth of emissions from coal.

Wrong options:

• sustaining: 'Sustaining' means to maintain or support, which contradicts the need to reduce emissions.
• dividing: 'Dividing' refers to separating into parts, which does not relate to the context of managing emissions.
• increasing: 'Increasing' means to make something larger or greater, which is the opposite of what is needed in terms of emissions management.