Trong phòng thí nghiệm có sẵn một dung dịch NaCl. Bằng phương pháp thực nghiệm, em hãy xác định dung dịch NaCl này là bão hòa hay chưa bão hòa. Trình bày cách làm.

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Exercise 3: Rewrite the following sentences as directed S+ haven’t/hasn’t + V3/V-ed since/ for = S+ last + V2/V-ed+ in/ on/ when/...ago = It's (khoảng tg) since S+ V2/V-ed = The last time S+ V2/V-ed was in/on/. 1. I haven’t seen her since she left school. I last ……………………………………………………………………............................... 2. We haven’t taken a vacation for two years. We last …………………………………………………………………………………......... 3. I haven’t played football since 1971. I last………………………………………………………………………………….............. 4. Lawrence hasn’t seen his sister since she left for Japan.  Lawrence last ………………………………………………………………………............ 5. We haven’t written to each other for two months. We last …………………………………………………………………………………......... 6. John hasn’t been back to his native village for nearly twenty years now. John was last …………………………………………………………………………………..... 7. Jerry hasn’t learned Spanish for three years. Jerry last …………………………………………………………………………………............ 8. Mrs. Lien hasn’t gone to the market since Monday.  Mrs. Lien last …………………………………………………………………………………. 9. I haven’t gone to Spain since 1998  I last.............................................................................................................................. 10. Sarah hasn’t seen her friends since she left for the US.  Sarah last................................................................................................... 11. The room hasn’t been used for a long time.  The room .................................................................................................... 12. I haven’t heard from him since he started work in Brazil.  I last............................................................................................................. 13. I haven’t seen Rosa for five years.  I last........................................................................................................ 14. The children haven’t gone to the dentist for six months.  The children last........................................................................................ 15. We haven’t gone to the cinema for over a year.  We last....................................................................................................