Meaning: An 'ingredient' is a substance that is part of a mixture or compound, in this case, referring to methane as a component of natural gas.

Wrong options:

• replenishing: Replenishing is a verb that means to restore or refill, which does not fit as it does not describe a component of natural gas.
• emits: Emits is a verb that refers to the act of releasing something, which does not fit as it does not describe a component of natural gas.
• stains: Stains is a noun that refers to marks or discolorations, which is unrelated to the context of organic molecules or natural gas.
• rejuvenating: Rejuvenating is a verb that means to make something look or feel younger, which does not fit the context of discussing organic molecules.
• concern: Concern is a noun that refers to a matter of interest or worry, which does not fit as it does not describe a component of natural gas.
• survives: Survives is a verb that means to continue to live or exist, which does not fit as it does not describe a component of natural gas.

Correct answer: survives

Explanation: The word 'survives' is a verb that fits grammatically and contextually, indicating the duration that methane can exist before it breaks down. It aligns with the scientific context of methane's characteristics.

Meaning: Survives means to continue to exist or live, particularly in reference to the lifespan of methane in the atmosphere.

Wrong options:

• replenishing: Replenishing is a verb that means to restore or refill, which does not fit as it does not describe the duration of existence of methane.
• ingredient: Ingredient is a noun that refers to a component of a mixture, which does not fit in the context of describing the lifespan of methane.
• emits: Emits is a verb that refers to the act of releasing something, which does not relate to the duration of methane's existence.
• stains: Stains is a noun that refers to marks or discolorations, which does not fit the context of discussing the lifespan of methane.
• rejuvenating: Rejuvenating is a verb that means to make something look or feel younger, which does not fit the context of methane's existence.
• concern: Concern is a noun that refers to a matter of interest or worry, which does not fit as it does not describe the lifespan of methane.

Correct answer: replenishing

Explanation: The word 'replenishing' is a verb that fits grammatically and contextually, indicating the action of restoring the supply of methane on Mars. It aligns with the idea that something is maintaining the methane levels.

Meaning: Replenishing means to restore or refill something that has been depleted, in this case, the supply of methane.

Wrong options:

• ingredient: Ingredient is a noun that refers to a component of a mixture, which does not fit as it does not describe an action related to methane supply.
• emits: Emits is a verb that refers to the act of releasing something, which does not fit as it does not describe the action of restoring methane.
• survives: Survives is a verb that means to continue to exist, which does not fit as it does not describe the action of restoring the supply of methane.
• stains: Stains is a noun that refers to marks or discolorations, which does not fit the context of discussing the restoration of methane supply.
• rejuvenating: Rejuvenating is a verb that means to make something look or feel younger, which does not fit the context of restoring methane supply.
• concern: Concern is a noun that refers to a matter of interest or worry, which does not fit as it does not describe an action related to methane.

Correct answer: emits

Explanation: The word 'emits' is a verb that fits grammatically and contextually, indicating the action of releasing methane from Mars. It aligns with the scientific context of methane production on the planet.

Meaning: Emits means to release or discharge something, in this case, referring to the release of methane from Mars.

Wrong options:

• replenishing: Replenishing is a verb that means to restore or refill, which does not fit as it does not describe the action of releasing methane.
• ingredient: Ingredient is a noun that refers to a component of a mixture, which does not fit in the context of describing the action of releasing methane.
• survives: Survives is a verb that means to continue to exist, which does not fit as it does not describe the action of releasing methane.
• stains: Stains is a noun that refers to marks or discolorations, which does not fit the context of discussing the release of methane.
• rejuvenating: Rejuvenating is a verb that means to make something look or feel younger, which does not fit the context of releasing methane.
• concern: Concern is a noun that refers to a matter of interest or worry, which does not fit as it does not describe the action of releasing methane.