Here are the closest meanings for the given sentences:

**Question 5:**
**Original sentence:** Phuong started to study English when he was in secondary school.
**Closest meaning:**
**D. Phuong studied English in secondary school.**
(Explanation: This choice indicates that Phuong was studying English during that time, which aligns with the original sentence.)

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**Question 6:**
**Original sentence:** “What subject do you like most?” Nam asked me.
**Closest meaning:**
**B. Nam asked me what subject I liked most.**
(Explanation: This choice correctly reflects the past tense used in the indirect question format, maintaining the meaning of the original sentence.)

If you have any other questions or need further clarification, feel free to ask!