A.I. Explanation:

Correct answer: harmful

Explanation: The word 'harmful' accurately describes the negative impact of toxic waste, fitting grammatically as an adjective that modifies 'residues' and contextually aligns with the overall sentiment of the sentence regarding the dangers of toxic waste.

Meaning: 'Harmful' means causing or capable of causing damage or injury, which is appropriate in the context of toxic waste residues.

Wrong options:

• painful: 'Painful' refers to physical or emotional suffering, which does not apply to the nature of waste residues.
• malicious: 'Malicious' implies intent to harm, which is not relevant to the description of waste residues themselves.
• cruel: 'Cruel' denotes a lack of compassion, which does not accurately describe the residues in a factual context.

Correct answer: up

Explanation: The phrase 'left up to' is a common idiomatic expression indicating that the responsibility or decision is assigned to someone, fitting grammatically and contextually within the sentence structure.

Meaning: 'Up' in this context means that the responsibility is given to these countries, indicating they must handle the situation.

Wrong options:

• on: 'On' does not convey the same meaning of responsibility and would not fit the idiomatic expression used here.
• by: 'By' suggests a method or means, which does not align with the intended meaning of assigning responsibility.
• for: 'For' implies purpose or benefit, which does not accurately reflect the context of responsibility being assigned.

Correct answer: according

Explanation: The word 'according' is used to reference information or rules, fitting grammatically as a preposition that introduces the legal context and aligns with the sentence's structure.

Meaning: 'According' means in agreement with or as stated by, which is appropriate when discussing legal matters.

Wrong options:

• admitting: 'Admitting' implies a confession, which does not fit the context of stating legal facts.
• agreeing: 'Agreeing' suggests a consensus, which is not relevant to the legal framework being referenced.
• stating: 'Stating' is a verb that does not fit grammatically in this context, as it does not introduce the legal reference correctly.

Correct answer: well-established

Explanation: The term 'well-established' describes principles that are recognized and accepted, fitting grammatically as an adjective that modifies 'principles' and contextually aligns with the idea of recognized legal standards.

Meaning: 'Well-established' means firmly established and widely accepted, which is suitable for describing principles in international law.

Wrong options:

• well-educated: 'Well-educated' refers to someone who has received a good education, which does not apply to principles.
• widely-dispersed: 'Widely-dispersed' suggests a physical distribution, which is not relevant to the nature of principles.
• widely-available: 'Widely-available' indicates accessibility, which does not accurately describe the nature of legal principles.