Giải thích:

`-` S `+` started/began `+` V-ing/to V0 `+` O `+` tgian trong quá khứ 

`=` S `+` have/has `+`  V3/V-ed `+` O `+` for + quãng tgian/since + mốc tgian

`=` S `+` have/has `+`  been `+` V-ing `+` O `+` for + quãng tgian/since + mốc tgian.. 

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`28,` We started learning English four years ago.

`29,` My father has given up smoking for a year.

`30,` He started collecting stamps five years ago.

`31,` She began working as a secretary after she left school.

`32,` Since `2005`, my old friend has worked on that farm. 

#$Ngọt<3$

`28`. We started learning English 4 years ago.

=> Cấu trúc TQKĐ: S + V_ed/V2.

=> Start + V_ing : Bắt đầu một cái gì đó.

`29`.My father has given up smoking for a year.

=> Cấu trúc THTHT: S + have/has + V_ed/V3.

=> For + mốc t/gian.

`30`.He started collecting stamps 5 years ago.

=> Cấu trúc : S + V_ed/V2.

=> Start + V_ing. : Bắt đầu làm gì đó.

`31.`She began working as a secretary after she left school.

=> Cấu trúc : S + V_ed/V2.

=> Began + V_ing : Bất đầu làm gì đó.

`32`.Since 2005,my old friend has worked on that farm. 

=> Cấu trúc : Since + Mốc t/gian.

=> Cấu trúc : S + have/has + V_ed/V3.