1. went -> go (- yesterday : ngày hôm qua -> Thì quá khứ đơn - thể phủ định: S + didn't + Vinf => went chuyển về dạng nguyên thể)

2. go -> went (- yesterday : ngày hôm qua -> Thì quá khứ đơn - thể khẳng định: S + Ved/ V2; go - went - gone: đi)

3. bought -> buy ( buy - bought - bought: mua )

4. weren't -> wasn't ( yesterday -> Thì quá khứ đơn - thể phủ định: S + were/ was + not  + ... ; "Paul" là ngôi số ít nên to be là "wasn't" )

5. sang -> sing ( sing - sang - sung: hát )

6. studies -> study ( Thì quá khứ đơn - thể nghi vấn: Did + S + Vinf?)

7. didn't -> weren't ( late (adj.) muộn là tính từ nên phải dùng to be )

8. not was -> was not

`1.` went `->` go 

`2.` go `->` went

`3.` bought `->` buy

`4.` weren't `->` wasn't 

`5.` sang `->` sing 

`6.` studies `->` study

`7.` didn't `->` weren't 

`8.` not was `->` was not

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`-` ÁP dụng:

`@` Thì quá khứ đơn:

`->` S + V2/ed + O

`->` S + did(not ) + V + O

`->` S + was/were (not) + V + O.