Read the passage about a climate agreement carefully and choose the adjective that correctly completes the phrase the first year of its ______ implementation.

Introduction / Context:
This question continues the cloze passage about an international climate agreement. The sentence refers to the first year of its ______ implementation, and the missing word must describe the type of implementation being discussed. In the context of treaties and international policies, it is common to speak about proposed implementation plans before they are fully carried out. This question therefore checks your understanding of related nouns and adjectives such as proposal, proposition, supposed and proposed.

Given Data / Assumptions:

• Sentence fragment: the first year of its ______ implementation.
• Options: proposal, proposition, supposed, proposed.
• The implementation relates to a climate agreement that has been designed but not yet fully carried out.
• We need an adjective that correctly modifies implementation in this formal context.

Concept / Approach:
The noun proposal describes a suggestion or plan put forward for consideration. Proposition also refers to a statement or scheme, often in business or logic. Supposed is an adjective meaning assumed or believed, sometimes with a doubtful tone. Proposed is the past participle of propose and commonly functions as an adjective that describes something that has been put forward as a plan. In the phrase proposed implementation, the word proposed neatly indicates that the implementation is planned but not yet completed. Therefore, proposed is the only option that fits both grammatically and contextually.

Step-by-Step Solution:
Step 1: Identify the grammatical role of the blank. It must be an adjective modifying implementation. Step 2: Evaluate proposal. This is a noun and does not fit directly before implementation without creating an awkward phrase. Step 3: Evaluate proposition. This is also a noun and does not form a natural collocation with implementation. Step 4: Evaluate supposed. Although it is an adjective, supposed implementation carries a doubtful tone, which is not typical in neutral treaty language. Step 5: Evaluate proposed. It is both grammatically correct as an adjective and contextually appropriate, meaning planned or suggested implementation.

Verification / Alternative check:
Read the sentence with each option. The first year of its proposal implementation sounds incorrect and unnatural. The first year of its proposition implementation is even more awkward. The first year of its supposed implementation hints that the implementation may not be real or accepted, which is not the intended neutral description in a treaty passage. In contrast, the first year of its proposed implementation closely matches the language used in policy reports and international documents. This confirms proposed as the correct choice.

Why Other Options Are Wrong:

• proposal: A noun that cannot directly modify implementation without additional structure, and the phrase proposal implementation is not standard.
• proposition: Also a noun, and proposition implementation is not an accepted collocation in formal writing.
• supposed: While grammatically possible, it introduces doubt or scepticism that does not fit the neutral descriptive tone of the passage.

Common Pitfalls:
Some students may confuse proposal and proposed because they share the same root. The key difference is that proposal is the thing suggested, while proposed is the adjective describing that thing or action. In exam passages about international policy, proposed reforms, proposed measures and proposed implementation are frequent phrases. Reading editorial and policy writing helps you become familiar with these patterns, making cloze questions like this much easier.

Final Answer:
The correct word is proposed, giving the phrase the first year of its proposed implementation.