She asked Ba if he had been reading that book at 88 o'clock the previous Sunday. 

∙∙ Câu gián tiếp dạng Yes/ No questions:

S+asked+O+if/whether+S+V(BackS+asked+O+if/whether+S+V(Back tense)+Otense)+O

∘∘ Lùi thì: QK tiếp diễn →→ QK hoàn thành tiếp diễn.

∘∘ Đổi chủ ngữ: you →→ he.

∘∘ This →→ that.

∘∘ Last Sunday →→ the previous Sunday.