In the following passage about the working of a pump stove that uses kerosene, some of the words have been left out. Read the passage carefully and select the correct answer for the given blank from the four alternatives. To lower the flame, the valve had to be _________ opened to reduce the pressure and then tightened until the desired flame size was achieved. In this question you must decide how far the valve is opened in the phrase the valve had to be _________ opened to reduce the pressure.

Introduction / Context:
This blank is also taken from the same explanatory passage that describes how to control the flame on a kerosene pump stove. The sentence focuses on adjusting the pressure by opening a valve. The test here is to identify the correct adverb that describes the degree to which the valve must be opened. This is a vocabulary and collocation based question with a clear mechanical context, typical of general English comprehension for competitive examinations.

Given Data / Assumptions:

• We are adjusting a valve on a pressurised kerosene stove.
• The purpose of opening the valve is to reduce pressure and lower the flame.
• The sentence fragment is the valve had to be _________ opened to reduce the pressure.
• Options are partly, some, none, and everything.
• The context suggests that the valve is opened a little, not fully, so that the pressure reduces gradually.

Concept / Approach:
The word partly is an adverb that means to some extent but not completely. When you open a valve partly, you open it a little to allow controlled release. The other words given are either determiners or pronouns and do not fit grammatically in this position. In natural English we say partly opened or partially opened. Therefore, partly is the only option that correctly modifies opened and matches the idea of controlled reduction of pressure.

Step-by-Step Solution:
Step 1: Identify the verb phrase had to be opened and note that a word before opened will describe the manner or extent of this action. Step 2: Recognise that we need an adverb of degree, telling us how far the valve is opened. Step 3: Examine the options. Partly is an adverb, while some, none, and everything are usually used as pronouns or determiners rather than adverbs. Step 4: Insert each option into the sentence: had to be partly opened, had to be some opened, had to be none opened, had to be everything opened. Step 5: See that only had to be partly opened is grammatically correct and expresses the required partial opening of the valve.

Verification / Alternative check:
You can confirm the choice by thinking of similar mechanical actions. For example, the door was partly opened, the lid was partly lifted, or the tap was partly turned. In each case, partly clearly expresses incomplete action. This matches the situation here, where the user carefully adjusts the valve instead of opening it fully. This comparison reinforces that partly is the correct and idiomatic word for this context.

Why Other Options Are Wrong:
some: Some is normally used before a noun, as in some water or some people. It does not fit directly before the past participle opened and cannot function here as an adverb. none: None means not any and is used as a pronoun or determiner, such as none of them. The phrase none opened is ungrammatical in this construction. everything: Everything is an indefinite pronoun referring to all things. The phrase everything opened makes no sense and cannot describe the degree to which a valve is opened.

Common Pitfalls:
Some learners may be tempted to over analyse the meaning of some or none and think that they convey partial or zero opening. However, in English grammar, these words cannot be used before opened in this passive construction. Remember to check both meaning and part of speech. Adjacent to a past participle, you usually need an adverb if you want to describe the extent of the action. Partly opened is a standard collocation; some opened or none opened are not used in standard English.

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