Meaning: 'Assumption' means something that is accepted as true or certain to happen without proof, in this case, the belief that the asteroids were completely dry.

Wrong options:

• process: 'Process' refers to a series of actions or steps taken to achieve a particular end, which does not fit the context of a belief about the asteroids.
• expansion: 'Expansion' implies an increase in size or scope, which is unrelated to the concept of a belief or idea regarding the asteroids' dryness.
• outline: 'Outline' refers to a general description or plan, which does not convey the idea of a belief or assumption about the asteroids.

Correct answer: which

Explanation: The word 'which' is a relative pronoun that introduces a non-defining clause, providing additional information about the SOFIA airborne telescope. It is grammatically correct and contextually relevant, linking the telescope to its function in detecting water signatures.

Meaning: 'Which' is used to refer to a specific thing or group of things, in this case, the SOFIA telescope that detected water signatures.

Wrong options:

• where: 'Where' indicates a place and does not fit the context of providing additional information about the telescope's function.
• whether: 'Whether' introduces alternatives or choices, which is not applicable in this context as it does not relate to the telescope's detection capabilities.
• that there: 'That there' is not a standard phrase and does not grammatically fit as a relative pronoun in this context.

Correct answer: comparable

Explanation: The word 'comparable' fits grammatically as it describes the amount of water in relation to that found on the lunar surface. It is contextually appropriate, indicating similarity in quantity, which aligns with the overall meaning of the sentence.

Meaning: 'Comparable' means similar in amount or quality, suggesting that the water found on the asteroids is similar to that found on the moon.

Wrong options:

• radical: 'Radical' implies something very different or extreme, which does not fit the context of comparing amounts of water.
• acceptable: 'Acceptable' refers to something that is satisfactory or permissible, which does not convey the idea of similarity in quantity.
• rational: 'Rational' means based on reason or logic, which does not relate to the comparison of amounts of water.

Correct answer: delivered

Explanation: The word 'delivered' fits grammatically as it indicates the action of providing or bringing something to a place. Contextually, it aligns with the idea that asteroids may have brought water to early Earth, making it a logical choice in the sentence.

Meaning: 'Delivered' means to bring or hand over something, in this case, water and elements to Earth through impacts.

Wrong options:

• reduced: 'Reduced' implies a decrease in size or amount, which does not fit the context of providing water to Earth.
• discovered: 'Discovered' refers to finding something for the first time, which does not relate to the action of bringing water to Earth.
• allocated: 'Allocated' means to distribute resources for a specific purpose, which does not convey the idea of bringing water through impacts.