In this passage completion question about a kerosene pump stove, choose the correct adverb to complete the clause: and ________ a small circular flame would appear in the burner.

Introduction / Context:
This question is part of a passage that describes the working of a kerosene pump stove. The sentence in focus explains how, after the fuel is under pressure, a small circular flame appears in the burner. The blank before a small circular flame would appear requires an adverb, because it is modifying the manner in which the flame appears. Understanding the difference between adjectives and adverbs is essential here.

Given Data / Assumptions:

• The target fragment is: and ________ a small circular flame would appear in the burner.
• The options are slow, slowly, slower, slowest.
• The sentence describes how the flame appears over time.
• The blank precedes the verb phrase would appear, so it should be filled by an adverb of manner.

Concept / Approach:
Adjectives describe nouns, while adverbs describe verbs, adjectives, or other adverbs. In this sentence, we are describing the manner in which the flame appears, which is an action. Therefore, an adverb form is needed. Slowly is the adverb that answers the question how does the flame appear. The other forms slow, slower, and slowest are adjectives or comparative and superlative forms and do not fit directly before a verb phrase in this structure.

Step-by-Step Solution:
Step 1: Identify that would appear is the verb phrase describing an action.Step 2: Recognise that a word placed just before the verb phrase and referring to the manner of appearance should be an adverb.Step 3: From the options, slowly is the standard adverb form, while slow is usually an adjective, and slower and slowest are comparative and superlative forms.Step 4: Insert each option in the sentence: and slow a small circular flame would appear, and slowly a small circular flame would appear, and slower a small circular flame would appear, and slowest a small circular flame would appear.Step 5: Notice that only and slowly a small circular flame would appear in the burner sounds natural and grammatically correct.Step 6: Select slowly as the correct answer.

Verification / Alternative Check:
You can verify the choice by comparing with similar sentences, such as Slowly, the clouds moved away or Slowly, the door opened. In all these cases an adverb is used before the verb to describe how the action happens. Replacing slowly with slow, slower, or slowest would break the grammar and produce unnatural English. This comparison confirms that slowly is the only acceptable option in this context.

Why Other Options Are Wrong:
Slow is primarily an adjective, used to describe nouns, for example a slow car or a slow process. It does not fit naturally before would appear without additional structure. Slower is the comparative form and would require a comparison, such as slower than before, which is not present in the sentence. Slowest is the superlative form and would also need a comparison among three or more things. None of these forms expresses the simple manner of appearance required here.

Common Pitfalls:
Many candidates see a familiar word like slow and choose it without checking whether an adjective or adverb is needed. Others misinterpret the sentence, assuming any form related to slow will work. A good strategy is always to ask what the word is modifying. If it modifies a verb, you almost always need an adverb. Keeping track of these basic grammar rules will help you avoid such traps in passage completion questions.

Final Answer:
The correct completion is: and slowly a small circular flame would appear in the burner.