We knew each other when we were in grade 7.

-> We .... ..... each other since we were in grade 7.

`-` We have known each other since we were in grade `7`.

`->` S + Ved + when + S + Ved

`=` S + have/has + P2 + since + S + Ved

`->` We/I/you/they `+` Have

`->` Chúng tôi quen nhau kể từ khi chúng tôi lớp 7`.

3. We have known each other since we were in grade 7. → Thì QKĐ (S + V2/ed) + when + Thì QKĐ (S + was/were + O)

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