`1.`Ba has studied English for three years

`-` Câu ở HTHT - for three years là DHNB, form: S + have/has + Vp.p + .. 

`2.` Why did Nam have to cook dinner himself

`-` Câu ở QKĐ, form: S + Ved/Vc2+ ... 

`3.` She asked me to spend more time on English

`-` Cấu trúc: ask sb to do sth = hỏi ai đó để làm gì

`4.` He used to go to school late last year

`-` Cấu trúc: S + used to + V-inf + ...

`1`: Ba has studied English for three years.

`->` DHNB:  for three years  - thì HTHT

`->` he , she , it + has + VpII

`2`: Why did Nam have to cook dinner himself?

`->` Why + did + S + Vinf ?

`->` have to + Vinf.

`->`Tại sao Nam phải tự nấu bữa tối?

`3`:  She asked me to spend more time on English

`->` S asked S.O to Vinf something

`->` Cô ấy yêu cầu tôi dành nhiều thời gian hơn cho tiếng Anh

`4`: He used to go to school late last year

`->` DHNB: last year - thì QKĐ

`=>` S + Ved/ V2

`->` used to Vinf