Meaning: 'Existence' refers to the state of living or being present, indicating the time dinosaurs were alive.

Wrong options:

• continuous: 'Continuous' is an adjective that describes something ongoing without interruption, which does not fit as a noun in this context.
• extent: 'Extent' refers to the range or scope of something, but it does not convey the idea of being alive or present, making it unsuitable here.
• expectation: 'Expectation' is a noun that refers to a belief about what will happen in the future, which is irrelevant to the context of dinosaurs' time on Earth.

Correct answer: went

Explanation: 'Went' is the simple past tense of 'go,' which correctly indicates that dinosaurs became extinct in the past, fitting the grammatical structure of the sentence.

Meaning: 'Went' means to have moved from one place to another, but in this context, it signifies that dinosaurs ceased to exist.

Wrong options:

• to go: 'To go' is an infinitive form and does not fit grammatically as it requires a helping verb to indicate past action.
• going: 'Going' is a present participle that does not fit the past context of extinction indicated in the sentence.
• go: 'Go' is the base form of the verb and does not match the past tense required in this context.

Correct answer: completely

Explanation: 'Completely' is an adverb that modifies the verb 'disappeared,' indicating the totality of the extinction event, which aligns with the context of the sentence.

Meaning: 'Completely' means entirely or fully, emphasizing that dinosaurs vanished without any remaining population.

Wrong options:

• partially: 'Partially' suggests that some dinosaurs survived, which contradicts the context of total extinction.
• gradually: 'Gradually' implies a slow process, which does not align with the sudden nature of the extinction event described.
• excessively: 'Excessively' indicates an overabundance, which is irrelevant and does not fit the context of extinction.

Correct answer: Although

Explanation: 'Although' is a conjunction that introduces a contrast, fitting the context of the sentence by indicating that despite the decline in species, a significant event still occurred.

Meaning: 'Although' means 'in spite of the fact that,' introducing a contrasting idea about the declining number of dinosaur species.

Wrong options:

• However: 'However' is typically used to introduce a statement that contrasts with a previous one, but it does not fit the grammatical structure needed here.
• Because: 'Because' indicates a reason, which does not align with the contrasting relationship intended in the sentence.
• Unless: 'Unless' introduces a conditional clause, which is not appropriate for the context of contrasting ideas.

Correct answer: open

Explanation: 'Open' is an adjective that describes the state of the debate, indicating that it is ongoing and not yet resolved, fitting the context of scientific inquiry.

Meaning: 'Open' means not closed or restricted, suggesting that the topic is still under discussion and exploration in the scientific community.

Wrong options:

• relative: 'Relative' refers to something considered in relation to something else, which does not apply to the state of a debate.
• additional: 'Additional' means extra or supplementary, which does not convey the idea of an unresolved debate.
• focused: 'Focused' implies concentration on a specific topic, which contradicts the idea of an ongoing debate that encompasses various viewpoints.

Correct answer: gradual

Explanation: 'Gradual' is an adjective that describes changes occurring slowly over time, fitting the context of climate changes that happened over millions of years.

Meaning: 'Gradual' means taking place slowly or in small steps, indicating that these changes were not sudden but rather progressive.

Wrong options:

• irregular: 'Irregular' suggests something that does not follow a consistent pattern, which does not accurately describe the nature of climate changes.
• spiritual: 'Spiritual' relates to religious or metaphysical matters, which is irrelevant to the context of environmental changes.
• positive: 'Positive' indicates something beneficial or good, which does not fit the context of climate changes that contributed to extinction.