Fill in the blank with the correct preposition to complete the idiomatic expression: “Put your own house _______ order before preaching others.”

Introduction:
This question tests your knowledge of a well known English idiom: put your own house in order. The expression is used to advise someone to correct their own faults or problems before criticising others. The challenge here is to choose the correct preposition that completes the fixed phrase and preserves its idiomatic meaning.

Given Data / Assumptions:

- Sentence: Put your own house _______ order before preaching others. - Options: within, into, in, to. - The idiom is widely used in spoken and written English.

Concept / Approach:
The correct form of the idiom is to put one's house in order. Here, house does not literally refer to a building, but to one's personal affairs, behaviour, or organisation. The preposition in is always used with order in this expression. Other prepositions like within, into, or to either change the meaning or do not fit the fixed idiom. Therefore, the correct answer is in.

Step-by-Step Solution:
Step 1: Recall the complete idiom from common usage: put your house in order. Step 2: Insert each option in the blank and test: Put your own house in order sounds familiar and correct. Step 3: Try within: Put your own house within order is ungrammatical and not an idiom. Step 4: Try into: Put your own house into order is understandable but not the fixed idiomatic expression. Step 5: Try to: Put your own house to order is not used in standard English. Step 6: Conclude that in is the only correct choice that completes the idiom.

Verification / Alternative check:
Consider similar phrases like bring something in order, set things in order, or keep your room in order. In each case, the preposition in is used with order to indicate an organised or correct state. The idiom put your house in order follows the same pattern. This consistency strengthens the conclusion that only in is appropriate here.

Why Other Options Are Wrong:
Within indicates inside the boundaries of something and does not typically form a phrase with order in this way. Into is used to indicate movement from outside to inside, which is not the point of the idiom. To is used in phrases like to order food or to put something to use, but not with house and order in this context. Because the question specifically targets a set idiom, any deviation from the standard form is incorrect.

Common Pitfalls:
Some learners overthink idioms and try to adjust prepositions according to literal meanings. However, idioms often follow fixed patterns that you must memorise, rather than derive logically. Reading good quality English and noting such phrases in context is an effective way to internalise them. When you encounter a familiar expression in a test, trust the version you have seen repeatedly rather than trying to invent a new variant.

Final Answer:
in is the correct preposition, giving the complete idiom put your own house in order.