Meaning: 'Produced' means to have created or generated something, in this case, greenhouse gas emissions.

Wrong options:

• add: 'Add' is a verb that means to join or combine, which does not fit the context of emissions being generated.
• pop: 'Pop' is a verb that typically refers to a sudden burst or sound, which is irrelevant in the context of emissions.
• transported: 'Transported' is the past participle of 'transport,' meaning to carry something from one place to another, which does not apply to the generation of emissions.
• tackle: 'Tackle' is a verb meaning to confront or deal with a problem, which does not fit as it does not describe the action of emissions being created.
• estimate: 'Estimate' is a verb that means to roughly calculate or judge the value, which does not relate to the production of emissions.

Correct answer: tackle

Explanation: The word 'tackle' is a verb that means to confront or deal with a problem, which fits contextually as it describes the efforts cities are making to address their emissions.

Meaning: 'Tackle' means to confront or take action to solve a problem.

Wrong options:

• add: 'Add' does not fit as it implies increasing something rather than addressing or solving an issue.
• pop: 'Pop' is unrelated to the context of addressing emissions and does not convey the intended meaning of action.
• produced: 'Produced' is a past participle that does not fit as it does not relate to the action of addressing emissions.
• estimate: 'Estimate' means to roughly calculate, which does not convey the action of dealing with emissions.
• transported: 'Transported' refers to carrying something, which is not relevant to the context of addressing emissions.

Correct answer: add

Explanation: The word 'add' is a verb that means to increase or contribute to something, which fits grammatically and contextually as it describes how trees and lawns contribute to the carbon-absorbing effect.

Meaning: 'Add' means to contribute or increase something.

Wrong options:

• pop: 'Pop' does not fit in this context as it does not relate to the contribution of trees and lawns to carbon absorption.
• produced: 'Produced' does not fit as it refers to creation rather than contribution in this context.
• tackle: 'Tackle' is about addressing a problem, which does not apply to the action of contributing to an effect.
• estimate: 'Estimate' means to calculate roughly, which does not relate to the action of contributing to an effect.
• transported: 'Transported' refers to carrying something, which is not relevant to the context of contributing to carbon absorption.