I said to him, "Why are you working so hard?"

Answer: Option A

Original Sentence (Direct Speech):
I said to him, "Why are you working so hard?"

Step-by-step Conversion:
1. This is a WH-question (starting with "Why"), so we keep the question word ("why") in indirect speech.
2. “Said to” changes to “asked” because it’s a question.
3. In indirect speech, question word order becomes statement order. So, “are you working” becomes “he was working”.
4. The tense of the verb "are working" (present continuous) changes to past continuous → “was working”.
5. The phrase “so hard” remains the same.

Correct Sentence:
I asked him why he was working so hard.

Correct Answer: Option A

Why other options are incorrect:
Option B: “why was he working” — ❌ wrong word order. In indirect speech, we don’t use question format.
Option C: “why had he been working” — ❌ wrong tense. Present continuous should change to past continuous, not past perfect continuous.
Option D: Same as Option C — ❌ wrong tense transformation.

Final Answer: Option A – I asked him why he was working so hard.