Meaning: 'Outdoors' refers to the open air or natural environment outside of buildings.

Wrong options:

• indoors: 'Indoors' refers to being inside a building, which contradicts the context of exploration in nature.
• break: 'Break' is a noun that typically refers to a pause or interruption, which does not fit the context of exploration.
• board: 'Board' is a noun that refers to a flat piece of material or the act of getting on a vehicle, which does not relate to the natural environment.
• sparing: 'Sparing' is an adjective that means limited or frugal, which does not fit the context of describing a place for exploration.
• growing: 'Growing' is an adjective that describes something that is increasing in size or amount, which does not apply to the context of the outdoors.
• become: 'Become' is a verb that indicates a change of state, which does not fit as a noun in this context.

Correct answer: board

Explanation: The term 'board' is used as a noun here, referring to the people present on the vessel. It fits grammatically and contextually as it indicates the experts who are present to give presentations.

Meaning: 'Board' refers to the group of people who are on a ship or other vehicle.

Wrong options:

• indoors: 'Indoors' does not fit as it refers to being inside a building, which is not relevant to the context of the ship.
• outdoors: 'Outdoors' refers to the natural environment outside, which does not apply to the context of people on the ship.
• break: 'Break' does not fit as it refers to a pause or interruption, which is unrelated to the context of experts presenting.
• sparing: 'Sparing' is an adjective that does not fit as it does not refer to people or a group.
• growing: 'Growing' is an adjective that does not apply to the context of people on the ship.
• become: 'Become' is a verb that does not fit as it does not refer to a group of people.

Correct answer: growing

Explanation: The word 'growing' is an adjective that describes the increasing importance or prevalence of the issue of Arctic sovereignty. It fits grammatically and contextually as it indicates that the debate is becoming more significant over time.

Meaning: 'Growing' means increasing in size, amount, or importance.

Wrong options:

• indoors: 'Indoors' does not fit as it refers to being inside a building, which is unrelated to the context of debate.
• outdoors: 'Outdoors' refers to the natural environment outside, which does not apply to the context of the debate.
• break: 'Break' does not fit as it refers to a pause or interruption, which is not relevant to the context of a cause of debate.
• board: 'Board' is a noun that does not apply to the context of describing a cause of debate.
• sparing: 'Sparing' is an adjective that means limited or frugal, which does not fit the context of describing a growing issue.
• become: 'Become' is a verb that does not fit as it does not describe the nature of the debate.

Correct answer: become

Explanation: The verb 'become' fits grammatically as it indicates a change in state, specifically that natural resources are transitioning to being accessible. This aligns with the context of the sentence discussing the implications of melting ice.

Meaning: 'Become' means to begin to be or to change into a particular state.

Wrong options:

• indoors: 'Indoors' does not fit as it refers to being inside a building, which is unrelated to the context of accessibility of resources.
• outdoors: 'Outdoors' refers to the natural environment outside, which does not apply to the context of resources becoming accessible.
• break: 'Break' does not fit as it refers to a pause or interruption, which is not relevant to the context of resources.
• board: 'Board' is a noun that does not apply to the context of describing a change in state of resources.
• growing: 'Growing' is an adjective that does not fit as it does not indicate a change in state.
• sparing: 'Sparing' is an adjective that means limited or frugal, which does not fit the context of resources becoming accessible.