In this reported speech question with a wh clause and a time expression, you must convert the direct question "The father said to the son, \"Why do you not start preparing for the examination this month?\"" into the correct indirect form.

Introduction / Context:
This question checks your competence in reporting a present simple wh question that includes a negative form and a time phrase referring to "this month". The direct question is "The father said to the son, 'Why do you not start preparing for the examination this month?'" You must select the indirect version that keeps the meaning while following standard rules for reported questions.

Given Data / Assumptions:

• Reporting clause: The father said to the son.
• Question: Why do you not start preparing for the examination this month?
• Wh word: Why, asking for the reason.
• Time expression: this month, which may shift in indirect speech.

Concept / Approach:
When converting a wh question to indirect speech, we change "said to" to "asked" or "enquired of", keep the wh word at the beginning of the subordinate clause, and use statement word order rather than question order. The auxiliary "do" is removed in indirect speech, and the main verb takes its correct past form if backshifting occurs. Since the reporting verb is in the past, "do you not start" becomes "he did not start". The expression "this month" typically becomes "that month" in reported speech.

Step-by-Step Solution:
Change "said to the son" to "asked the son".Keep the wh word "why" at the start of the reported clause.Change "you" to "he" to refer to the son.Backshift "do you not start" to "he did not start", removing the auxiliary "do".Change "this month" to "that month" to reflect indirect narration.Combine into: "The father asked the son why he did not start preparing for the examination that month."

Verification / Alternative check:
The complete sentence "The father asked the son why he did not start preparing for the examination that month." is grammatically correct and accurately conveys the same meaning as the original direct question. It follows the standard pattern for reporting wh questions with negation and time references.

Why Other Options Are Wrong:
Option A uses the ungrammatical structure "that why did he", which mixes a that clause with question word order. Option B uses "told" instead of "asked" and changes the time phrase incorrectly; it also drops the idea of "start preparing" and instead only says "did not prepare", which slightly distorts the nuance. Option C keeps "this month" unchanged, which is less appropriate for reported speech, and also suggests no backshift in the time reference, which exam keys usually expect to change.

Common Pitfalls:
A frequent mistake is to retain the question word order after the wh word, for example "why did he not start", instead of the correct "why he did not start" in indirect speech. Another common problem is forgetting to change demonstratives like "this" to "that" in reported clauses. It is helpful to mentally convert direct questions to statements after the wh word when forming indirect speech.

Final Answer:
The correct indirect sentence is The father asked the son why he did not start preparing for the examination that month.