Meaning: To 'shape' means to influence or determine the form or character of something.

Wrong options:

• degradation: 'Degradation' is a noun that refers to the process of something being damaged or deteriorated, which does not fit grammatically or contextually in this sentence.
• protection: 'Protection' is a noun that implies safeguarding, which does not convey the active role plants play in influencing the environment.
• simplify: 'Simplify' is a verb that means to make something easier to understand, which does not relate to the context of how plants affect the environment.
• power: 'Power' is a noun that refers to the ability to do something or act in a certain way, but it does not fit the grammatical structure of the sentence as it lacks a direct action related to the environment.
• source: 'Source' is a noun that indicates a point of origin, which does not fit the verb form needed in this context.

Correct answer: degradation

Explanation: The term 'degradation' is a noun that fits grammatically and contextually, referring to the decline or deterioration of the environment, which is one of the major challenges mentioned in the text.

Meaning: 'Degradation' refers to the process of something being damaged or reduced in quality, particularly in an environmental context.

Wrong options:

• shape: 'Shape' is a verb that does not fit grammatically as a noun in this context, and it does not relate to the challenges facing humanity.
• protection: 'Protection' is a noun that implies safeguarding, which does not accurately describe the challenges of environmental decline.
• simplify: 'Simplify' is a verb that means to make something easier, which does not relate to the context of environmental challenges.
• power: 'Power' is a noun that refers to the ability to do something, but it does not fit the context of environmental issues as a challenge.
• source: 'Source' is a noun that indicates a point of origin, which does not align with the context of environmental challenges.

Correct answer: source

Explanation: The word 'source' is a noun that fits grammatically in the sentence, indicating that plants are a fundamental origin of energy production. This aligns with the context of discussing the role of plants in energy and food production.

Meaning: A 'source' is a point of origin or supply from which something is obtained.

Wrong options:

• degradation: 'Degradation' is a noun that refers to decline or deterioration, which does not fit the context of describing plants' role in energy production.
• protection: 'Protection' is a noun that implies safeguarding, which does not relate to the context of energy production from plants.
• shape: 'Shape' is a verb that does not fit grammatically as a noun in this context, and it does not describe the role of plants in energy production.
• simplify: 'Simplify' is a verb that means to make something easier, which does not relate to the context of plants as a source of energy.
• power: 'Power' is a noun that refers to the ability to do something, but it does not fit the grammatical structure needed to describe plants' role.