Read the passage about a climate agreement carefully and choose the phrase that correctly completes the line The agreement will enter into force with the ratification of ______ 55 countries.

Introduction / Context:
This question is another part of the passage discussing the conditions under which a climate agreement will enter into force. The sentence states that the agreement will take effect after ratification by a certain number of countries. The missing phrase must express a minimum threshold rather than a vague or partial degree. Such wording is common in international treaties, which precisely specify that at least a certain number of parties must ratify the agreement for it to become legally binding.

Given Data / Assumptions:

• Sentence fragment: The agreement will enter into force with the ratification of ______ 55 countries.
• Options: partially, at least, slightly, somewhat.
• The context indicates a numeric threshold for ratification.
• The phrase must link naturally with 55 countries and describe a minimum requirement.

Concept / Approach:
The phrase at least is used to indicate a minimum number or quantity that must be reached or exceeded. It fits perfectly with a legal requirement such as the ratification of at least 55 countries. Words like partially, slightly and somewhat indicate degrees of intensity or extent, not a minimum number. They do not collocate naturally with a specific integer in formal treaty language. Therefore, at least is the clear and appropriate choice for this blank.

Step-by-Step Solution:
Step 1: Understand that the sentence is setting a numerical condition for the treaty to enter into force. Step 2: Recognise that we need a phrase that expresses a minimum threshold. Step 3: Evaluate partially. It modifies how much something is done, not the number of countries. Step 4: Evaluate at least. It directly expresses the idea that 55 is the minimum number required. Step 5: Evaluate slightly and somewhat, which again refer to small degrees and are not used to qualify a specific cardinal number in this way.

Verification / Alternative check:
Read the sentence with each option. The agreement will enter into force with the ratification of partially 55 countries is ungrammatical. The agreement will enter into force with the ratification of slightly 55 countries also sounds wrong and meaningless. The agreement will enter into force with the ratification of somewhat 55 countries is equally incorrect. In contrast, the agreement will enter into force with the ratification of at least 55 countries is grammatically correct and matches the way such conditions are described in international texts. This confirms that at least is the only suitable option.

Why Other Options Are Wrong:

• partially: Describes incomplete extent, not a minimum count of countries; it cannot be directly followed by a number in this structure.
• slightly: Indicates a small degree or amount, not a threshold number; slightly 55 countries is not a valid phrase.
• somewhat: Also refers to degree or extent in a vague way, and cannot be used with a precise count like 55.

Common Pitfalls:
Students may be tempted by partially because treaties sometimes talk about partial implementation or partial compliance. However, those phrases do not take exact numbers in the same way. Another mistake is to focus only on the positive sounding phrases without considering grammar. Whenever a number is given, check whether the surrounding words are capable of specifying a minimum, maximum or approximate amount. The phrase at least is very common for setting lower bounds and should be recognised quickly in exam passages.

Final Answer:
The correct phrase is at least, yielding The agreement will enter into force with the ratification of at least 55 countries.