Một hình thang có S=90 m2, hiệu của 2 đáy là 6m. Tính độ dài mỗi đáy biết nếu đáy lớn tăng thêm 2m thì S hình thang tăng thêm 8m2.

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Exercise II:Change the following sentences into the passive voice :Yes – No questions: 1. Do they teach English here?……………………………………………………… 2. Will you invite her to your wedding party?……………………………………… 3. Did the teacher give some exercises?…………………………………………………… 4. Is he going to write a poem?………………………………………………………… 5. Have they changed the window of the laboratory?…………………………………… 6. Is Tom making big cakes for the party?………………………………………… 7. Must we finish the test before ten?………………………………………………… 8. Are the police making inquires about the thief?………………………………………… Exercise III:Change the following sentences into the passive voice : Wh-question: 1. When will you do the work? ……………………………………………………………. 2. How many days did she spend finishing the work? …………………………………………… 3. Why didn’t they help him? …………………………………………………………….. 4. Who are they keeping in the kitchen? …………………………………………………. 5. Who did the police find the lost man? …………………………………………………. 6. Who looked after the children for you?…………………………………………………. Exercise IV: Change the following sentences into the active voice : Sentences of imperative: 1. Open your book. ………………………………………………………………………. 2. Take off your hat!……………………………………………………………………. 3. Don’t do that silly thing again!………………………………………… 4. let’s tell them about it!………………………………………………… 5. Don’t let the other see you. …………………………………………………