Meaning: 'Designated' means officially assigned or marked for a specific purpose, in this case, recognizing the koala as a threatened species.

Wrong options:

• welcomed: 'Welcomed' implies acceptance or approval, which does not fit the context of classifying a species.
• submitted: 'Submitted' suggests presenting something for consideration, which is not relevant to the official classification of a species.
• celebrated: 'Celebrated' means to honor or commemorate, which is inappropriate in the context of a species being classified as threatened.

Correct answer: substantial

Explanation: The term 'substantial' appropriately describes a significant or considerable number of koalas, fitting both grammatically and contextually within the sentence discussing their struggles with diseases.

Meaning: 'Substantial' means considerable in quantity or importance, indicating that the number of affected koalas is significant.

Wrong options:

• main: 'Main' suggests primary importance, which does not accurately convey the idea of quantity in this context.
• permanent: 'Permanent' implies lasting or unchanging, which does not relate to the number of koalas grappling with diseases.
• vital: 'Vital' means essential or necessary, but it does not convey the idea of quantity as effectively as 'substantial'.

Correct answer: criteria

Explanation: The word 'criteria' is the correct plural noun that refers to the standards or principles used for classification, fitting grammatically and contextually in the sentence about labeling species.

Meaning: 'Criteria' are the standards or rules by which something is judged or decided, in this case, the conditions for labeling a species as vulnerable.

Wrong options:

• climates: 'Climates' refers to weather conditions and does not relate to the standards for species classification.
• relations: 'Relations' implies connections or associations, which is not relevant to the context of species criteria.
• phenomena: 'Phenomena' refers to observable events or occurrences, which does not fit the context of classification standards.

Correct answer: observed

Explanation: The word 'observed' is the correct past participle that fits grammatically and contextually, indicating a decline that has been noted in Queensland, aligning with the sentence structure.

Meaning: 'Observed' means noticed or seen, referring to the decline in koala populations that has been recorded.

Wrong options:

• observing: 'Observing' is a present participle that does not fit the past tense context of the sentence.
• that observed: 'That observed' is grammatically incorrect as it does not properly connect to the preceding clause.
• which observing: 'Which observing' is also grammatically incorrect and does not fit the context of describing a past event.

Correct answer: deemed

Explanation: The word 'deemed' fits grammatically and contextually as it indicates an official judgment or classification regarding the koalas' risk status, aligning with the formal tone of the sentence.

Meaning: 'Deemed' means considered or regarded in a specified way, in this case, not considered at risk.

Wrong options:

• normalized: 'Normalized' implies making something standard or typical, which does not fit the context of risk classification.
• stored: 'Stored' means kept or saved, which is irrelevant to the classification of species.
• represented: 'Represented' suggests being depicted or symbolized, which does not accurately convey the idea of risk assessment.