=>
9. The teacher asked his student if she knew how to reduce garbage in public.
10. Tim asked Nancy if she was doing her math homework then.
11. The old woman asked me when the train S9 to Ho Chi Minh city left.
12. Huong asked Nam if his house was near Ben Thuy Bridge.
Câu tường thuật dạng Yes/No questions : asked sb if S V(lùi thì)
HTĐ -> QKĐ
HTTD -> QKTD

9. The teacher asked his student if he knew how to reduce garbage in public

10. Tim asked Nancy if she was doing her Math homework then

11. The old woman asked me when the train S9 to HCM City left

12. Huong asked Nam if his house was near Ben Thuy Bridge 

*Yes - No question: S + asked + (O) + if/ whether + S + V

*Wh - question: S asked + (O) + question word + S + V

*Lùi thì:

QKĐ → QKHT

HTĐ → QKĐ

HTHT → QKHT

HTTD → QKTD

QKTD → QKHTTD

HTHTTD → QKHTTD

will → would

can → could

may → might 

must → had to