Meaning: 'Renewable' refers to energy sources that are replenished naturally, such as solar energy.

Wrong options:

• clean: 'Clean' is an adjective that describes something free from pollutants, but it does not specifically indicate the type of electricity as 'renewable' does.
• footprint: 'Footprint' is a noun that refers to the impact or effect of something, which does not fit as a descriptor for electricity.
• thermal: 'Thermal' is an adjective related to heat, which does not apply to the context of electricity generation from solar energy.

Correct answer: footprint

Explanation: The term 'footprint' is used as a noun to describe the environmental impact of buildings. It fits contextually as it relates to carbon emissions and energy efficiency.

Meaning: 'Footprint' refers to the environmental impact or carbon emissions associated with a particular activity or entity.

Wrong options:

• clean: 'Clean' does not fit as it does not refer to a measurable impact like 'footprint' does.
• mental: 'Mental' is an adjective that relates to the mind, which does not apply to environmental impact.
• thermal: 'Thermal' refers to heat and does not relate to the concept of carbon emissions.

Correct answer: mental

Explanation: The word 'mental' serves as an adjective that describes the quality of well-being related to the mind. It fits contextually as it highlights the psychological benefits of green spaces.

Meaning: 'Mental' refers to aspects related to the mind or psychological state.

Wrong options:

• clean: 'Clean' does not fit as it describes physical cleanliness rather than psychological quality.
• footprint: 'Footprint' is a noun that refers to environmental impact, which does not relate to the quality of city dwellers' mental state.
• thermal: 'Thermal' pertains to heat and does not apply to mental quality.

Correct answer: electric

Explanation: The term 'electric' is an adjective that describes vehicles powered by electricity. It fits grammatically and contextually as it relates to reducing air pollution.

Meaning: 'Electric' refers to vehicles that operate on electric power rather than fossil fuels.

Wrong options:

• clean: 'Clean' does not specifically describe the type of vehicles as 'electric' does.
• footprint: 'Footprint' is a noun that does not apply to the description of vehicles.
• mental: 'Mental' relates to the mind and does not pertain to vehicles.