Meaning: 'Range' refers to a variety or selection of different things, in this case, the different types of research facilities available on the ships.

Wrong options:

• strange: 'Strange' is an adjective that describes something unusual or odd, which does not fit the context of describing facilities.
• rage: 'Rage' is a noun that refers to intense anger, which is irrelevant in this context and does not fit grammatically.
• stage: 'Stage' can refer to a phase or level, but it does not convey the idea of variety or extent needed in this context.

Correct answer: was challenged

Explanation: The phrase 'was challenged' is in the past tense, which is appropriate here as it refers to a historical trend that faced difficulties. The singular subject 'trend' requires the singular verb form 'was,' making it grammatically correct and contextually relevant.

Meaning: 'Was challenged' means that the trend faced difficulties or obstacles in adapting to the demands of complex oceanographic research.

Wrong options:

• was a challenge: This phrase is grammatically incorrect in this context as it does not fit the structure needed for the sentence; it suggests a noun phrase rather than a verb phrase.
• were challenged: This option is incorrect because 'were' is plural, while 'trend' is singular, creating a subject-verb agreement error.
• will have been challenged: This future perfect tense is inappropriate here as the context is discussing a past trend, not a future event.

Correct answer: out

Explanation: The phrase 'carry out' is a common collocation meaning to perform or conduct an action. It fits grammatically and contextually as it indicates the execution of multi-disciplinary research.

Meaning: 'Out' in this context is part of the phrasal verb 'carry out,' which means to perform or execute a task or research.

Wrong options:

• over: 'Over' does not fit the context as it does not convey the idea of performing or executing research.
• of: 'Of' is a preposition that does not create a meaningful phrase in this context and does not indicate action.
• through: 'Through' suggests movement within something rather than the execution of an action, making it unsuitable here.

Correct answer: will remain

Explanation: The phrase 'will remain' is in the future tense, indicating that research ships will continue to be the primary source of observations. This fits grammatically and contextually as it discusses future expectations.

Meaning: 'Will remain' means that something is expected to continue to exist or be true in the future.

Wrong options:

• will have remained: This future perfect tense is not suitable here as it implies a completed action in the future, which does not fit the context of ongoing observations.
• remaining: 'Remaining' is a present participle that does not fit the grammatical structure needed in this sentence.
• remains: 'Remains' is present tense and does not align with the future context of the sentence.

Correct answer: goes on

Explanation: The phrase 'goes on' is a common idiomatic expression meaning to continue or persist. It fits grammatically and contextually as it describes the ongoing passage of time.

Meaning: 'Goes on' means to continue or to keep happening, indicating the progression of time.

Wrong options:

• flies away: This phrase suggests a sudden departure and does not convey the idea of time passing, making it contextually irrelevant.
• disappears: 'Disappears' implies something ceasing to exist, which does not fit the context of time continuing.
• moves: While 'moves' could imply progression, it is less idiomatic and does not convey the same sense of continuity as 'goes on'.