In this passage completion question about a kerosene pump stove, choose the adverb that correctly completes the phrase: the valve had to be ________ opened to reduce the pressure.

Introduction / Context:
The passage explains how to control the flame of a kerosene pump stove by adjusting a valve. To reduce the pressure and lower the flame, the valve should not be opened fully but only to a limited extent. The sentence in focus states that the valve had to be blank opened to reduce the pressure. Your task is to choose the word that accurately describes this partial opening in natural English.

Given Data / Assumptions:

• The relevant fragment is: the valve had to be ________ opened to reduce the pressure.
• The options are partly, some, none, everything.
• The context suggests a controlled, limited opening of the valve, not a complete one.
• The blank must fit grammatically before the past participle opened.

Concept / Approach:
An adverb of degree is needed to describe how much the valve is opened. Partly is an adverb that means to some extent but not completely. It fits perfectly with opened to communicate that the valve is opened only a little. The other words either do not function correctly as adverbs in this structure or do not make sense in combination with opened. Therefore, recognising the intended meaning of partial opening leads directly to the correct choice.

Step-by-Step Solution:
Step 1: Determine that the sentence describes the valve being opened only a little to reduce pressure.Step 2: Identify the grammatical role of the blank. It modifies the verb phrase had to be opened and therefore should be an adverb of degree.Step 3: Evaluate partly, which means to some extent but not completely. This clearly matches the idea of limited opening.Step 4: Check some, which is normally used as a determiner before nouns, not as an adverb directly before opened in this way.Step 5: Consider none and everything, which express extremes and are not used as adverbs before opened in this structure.Step 6: Conclude that partly is the only option that both fits grammatically and matches the meaning.

Verification / Alternative Check:
Construct similar sentences to verify the pattern, such as The window had to be partly opened to let in some air or The tap is partly opened to control the flow. These sentences sound natural and mirror the structure of the exam sentence. If you try replacing partly with some, none, or everything, the results are ungrammatical or do not convey the same idea. This comparison confirms that partly opened is the correct collocation.

Why Other Options Are Wrong:
Some is typically used with countable or uncountable nouns, as in some water or some people, and does not function as an adverb before a past participle here. None indicates zero quantity and would imply that the valve is not opened at all, which contradicts the need to open it slightly to reduce pressure. Everything refers to all things collectively and does not work semantically or grammatically in this phrase. Consequently, these options cannot express the intended partial opening of the valve.

Common Pitfalls:
Candidates sometimes choose some because they associate it with partial quantities, but they overlook that it does not combine correctly with opened in this sentence. Others may be confused by the presence of extreme words like none and everything, but these are distractions designed to test careful reading. Always ensure that the chosen word fits both the grammatical role and the practical meaning that the passage requires.

Final Answer:
The correct completion is: the valve had to be partly opened to reduce the pressure.