Meaning: 'Them' is used to refer to multiple items previously mentioned, in this case, the distances.

Wrong options:

• their: 'Their' is a possessive pronoun that indicates ownership, which does not fit here as it does not refer to the distances directly.
• least: 'Least' is an adverb that indicates the smallest amount, which does not fit grammatically in this context.
• get: 'Get' is a verb that does not serve as a pronoun and does not fit in this sentence.
• over: 'Over' is a preposition that indicates a position above something, which does not fit the context of referring to distances.
• in: 'In' is a preposition that indicates inclusion within something, which does not fit as a pronoun here.
• on: 'On' is a preposition that indicates a position atop something, which does not fit as a pronoun in this context.

Correct answer: on

Explanation: The preposition 'on' is used to indicate a position or state, which fits grammatically and contextually as it describes the scale of distances being discussed.

Meaning: 'On' indicates a position or state, in this case, referring to the scale of distances.

Wrong options:

• their: 'Their' is a possessive pronoun that does not fit as it does not indicate a position or state.
• least: 'Least' is an adverb that indicates the smallest amount, which does not fit in this context.
• get: 'Get' is a verb that does not relate to the scale of distances and does not fit grammatically.
• over: 'Over' is a preposition that indicates a position above something, which does not fit the context of scale.
• in: 'In' is a preposition that indicates inclusion within something, which does not fit the context of scale here.
• don't: 'Don't' is a contraction for 'do not,' which does not fit as a preposition.

Correct answer: get

Explanation: The verb 'get' is used here to indicate the action of obtaining or acquiring a sense of understanding, which fits grammatically and contextually in the sentence.

Meaning: 'Get' means to obtain or understand something.

Wrong options:

• their: 'Their' is a possessive pronoun that does not fit as a verb in this context.
• least: 'Least' is an adverb that indicates the smallest amount, which does not fit as a verb here.
• on: 'On' is a preposition that does not convey an action and does not fit grammatically.
• over: 'Over' is a preposition that indicates a position above something, which does not fit as a verb.
• in: 'In' is a preposition that does not convey an action and does not fit in this context.
• don't: 'Don't' is a contraction for 'do not,' which does not fit as a verb.

Correct answer: don't

Explanation: The contraction 'don't' is used to express a negation, fitting grammatically and contextually as it conveys the idea of not losing hope regarding future technological advancements.

Meaning: 'Don't' is a contraction for 'do not,' used to indicate negation.

Wrong options:

• their: 'Their' is a possessive pronoun that does not fit as a verb in this context.
• least: 'Least' is an adverb that indicates the smallest amount, which does not fit as a verb here.
• get: 'Get' is a verb that does not convey negation and does not fit grammatically.
• over: 'Over' is a preposition that does not fit as a verb in this context.
• in: 'In' is a preposition that does not convey negation and does not fit here.
• on: 'On' is a preposition that does not fit as a verb.

Correct answer: least

Explanation: The word 'least' is used as an adverb to indicate the minimum degree or amount, which fits grammatically and contextually in the sentence discussing the feasibility of interstellar travel.

Meaning: 'Least' refers to the smallest amount or minimum degree.

Wrong options:

• their: 'Their' is a possessive pronoun that does not fit as an adverb in this context.
• don't: 'Don't' is a contraction for 'do not,' which does not fit as an adverb here.
• get: 'Get' is a verb that does not convey a degree or amount and does not fit grammatically.
• over: 'Over' is a preposition that does not fit as an adverb in this context.
• in: 'In' is a preposition that does not convey a degree or amount and does not fit here.
• on: 'On' is a preposition that does not fit as an adverb.