In this passage completion question about a kerosene pump stove, choose the conjunction that correctly begins the clause: ________ you wanted the flame to be bigger, you had to hit the piston again.

Introduction / Context:
The passage describes how the user can control the size of the flame in a kerosene pump stove. After explaining how to lower the flame, it explains what to do when a bigger flame is desired. The sentence in focus states that blank you wanted the flame to be bigger, you had to hit the piston again. This blank must be filled with a conjunction that introduces a condition and leads naturally into the result described in the second part of the sentence.

Given Data / Assumptions:

• The sentence fragment is: ________ you wanted the flame to be bigger, you had to hit the piston again.
• The options are If, Nor, So, Thus.
• The first clause describes a condition related to wanting a bigger flame.
• The second clause explains the action required when that condition is true.

Concept / Approach:
In English, conditional sentences usually begin with if when introducing a condition that leads to a particular result, as in If you want this, you must do that. The structure here clearly fits a conditional pattern: when or in case you want a bigger flame, you must hit the piston again. Therefore, If is the natural choice. The other options serve different logical functions, such as expressing contrast, continuation, or consequence, and do not introduce a condition in the same way.

Step-by-Step Solution:
Step 1: Recognise that the second half of the sentence describes what you must do when a certain condition is met.Step 2: Understand that the condition is wanting the flame to be bigger.Step 3: Recall that conditional clauses of this type are normally introduced by if in standard English.Step 4: Insert If into the sentence: If you wanted the flame to be bigger, you had to hit the piston again. This reads naturally and clearly.Step 5: Test the alternatives: Nor you wanted the flame, So you wanted the flame, Thus you wanted the flame. All of these are awkward and incorrect.Step 6: Confirm that If is the only conjunction that correctly signals a condition in this context.

Verification / Alternative Check:
Compare this sentence with other conditional instructions, such as If you feel cold, put on a sweater or If you want more light, switch on another lamp. In each case, if introduces the condition and the main clause gives the resulting action. This pattern matches exactly with If you wanted the flame to be bigger, you had to hit the piston again. Replacing if with nor, so, or thus breaks the logic and the grammar, confirming our choice.

Why Other Options Are Wrong:
Nor is used to connect negative clauses in expressions such as neither this nor that and cannot start a positive conditional statement here. So usually introduces a result, for example It was raining, so we stayed inside, and not the condition itself. Thus also introduces a conclusion or result, similar to therefore, and does not fit naturally at the start of a conditional clause. None of these words functions like if in standard conditional sentence structures.

Common Pitfalls:
Some students overcomplicate the sentence and search for a more formal connector like thus, forgetting that the structure is a simple condition and result. Others misread the sentence and think it is giving a direct instruction rather than presenting a conditional scenario from past practice. Remember to identify whether the first clause expresses a condition, reason, or result before choosing a conjunction, and you will reliably avoid these traps.

Final Answer:
The correct beginning is: If you wanted the flame to be bigger, you had to hit the piston again.