Meaning: 'Covered' means to be placed over or to be protected by something, in this case, liquid water and ice.

Wrong options:

• availability: 'Availability' is a noun that refers to the state of being able to be used or obtained, which does not fit grammatically as it does not describe the state of the Earth's surface.
• extraction: 'Extraction' is a noun that refers to the act of removing something, which does not fit in the context of describing the Earth's surface.
• susceptibility: 'Susceptibility' is a noun that refers to the likelihood of being influenced or harmed by something, which does not relate to the description of the Earth's surface.
• edited: 'Edited' is the past participle of 'edit,' which means to make changes to something, and does not fit the context of describing the Earth's surface.
• redundantly: 'Redundantly' is an adverb that means in a way that is not necessary or superfluous, which does not fit grammatically or contextually.

Correct answer: constantly

Explanation: The adverb 'constantly' describes the continuous nature of water movement, fitting grammatically as it modifies the verb 'moving.' This aligns with the context of discussing the ongoing processes involving water in the atmosphere, land, and ocean.

Meaning: 'Constantly' means happening all the time or continuously without interruption.

Wrong options:

• availability: 'Availability' is a noun that does not fit grammatically as it cannot modify the verb 'moving.'
• extraction: 'Extraction' is a noun that refers to the act of removing something, which does not relate to the action of water movement.
• susceptibility: 'Susceptibility' is a noun that does not fit as it cannot describe the manner of movement.
• covered: 'Covered' is a past participle that does not function as an adverb and does not describe the nature of movement.
• edited: 'Edited' is a past participle that does not fit as it does not describe the action of water movement.
• redundantly: 'Redundantly' is an adverb that implies unnecessary repetition, which does not fit the context of continuous movement.

Correct answer: extraction

Explanation: The noun 'extraction' refers to the act of removing or taking out, which fits grammatically as it serves as the subject of the sentence. This aligns with the context of discussing human activities related to water use.

Meaning: 'Extraction' means the process of removing something, in this case, water from natural sources.

Wrong options:

• availability: 'Availability' is a noun that refers to the state of being able to be used or obtained, which does not fit as it does not describe an action related to water use.
• susceptibility: 'Susceptibility' is a noun that refers to the likelihood of being affected by something, which does not relate to the action of using water.
• covered: 'Covered' is a past participle that does not fit as it does not describe an action or process related to water.
• edited: 'Edited' is a past participle that does not fit in this context as it does not relate to the extraction or use of water.
• constantly: 'Constantly' is an adverb that describes the manner of an action, not an action itself, and does not fit here.

Correct answer: availability

Explanation: The noun 'availability' refers to the state of being able to be used or obtained, which fits grammatically as it serves as the object of the sentence. This aligns with the context of discussing the reduction of freshwater resources.

Meaning: 'Availability' means the quality of being able to be used or accessed, particularly in reference to freshwater resources.

Wrong options:

• extraction: 'Extraction' is a noun that refers to the act of removing something, which does not fit as it does not describe the state of freshwater resources.
• susceptibility: 'Susceptibility' is a noun that refers to the likelihood of being affected by something, which does not relate to the concept of resource availability.
• covered: 'Covered' is a past participle that does not fit as it does not describe a state of being or resource.
• edited: 'Edited' is a past participle that does not fit in this context as it does not relate to the availability of resources.
• constantly: 'Constantly' is an adverb that describes the manner of an action, not a state of being, and does not fit here.