cho hình thang cân abcd ab song song với cd và ab bé hơn cd kẻ các đường cao ah và bk của hình thang a chứng minhdh=ck b.gọi m là trung điểm của ad và n là trung điểm của bc.mn là lần lượt cắt bd tại e và ac tại f biết ab=4cm cd=10cm.tính EF

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EXERCISE: Put the verbs in brackets in the correct tense 1. The war (break) ___________ out three years ago. 2. I saw a bad accident while I (wait) __________ for you on this corner. 3. She (stay) ___________ with her sister at the moment until she finds somewhere to live. 4. The manager just (close) __________ the store the moment before I (arrive) ___________. 5. If you call her at 6, she (practice) ____________ the piano then. 6. When we (see) ___________ Mr. Taylor tomorrow, I (remind) ____________ him of that. 7. Up to the present, George (do) ____________ good work in this class. 8. My parents (live) ___________ in London. They (be) ____________ there for 20 years. 9. He (sit) _____________ in the garden when the house (fall) ___________ down. 10. At three o’clock this morning, Mary (study) _________ English. 11. They (build) ___________ that bridge when I was here last year. They (not finish) ___________ it yet. 12. He certainly (not, do) _____________ all his homework by 10 tonight. 13. Don’t make noise. My mother (talk) ___________ with her friends. 14. Miss Helen (help) ___________ you as soon as she (finish) _____________ that letter tomorrow. 15. He (do) ___________ his homework before he went to the cinema. 16. The moon (go) ___________ round the earth. 17. I feel terrible. I think I (be) ______________ sick. 18. He (leave) _____________ London 2 years ago and I (not/ see) ____________ him since then. 19. Where ___________ you (live) __________? – In a flat, near the university. 20. When he (return) ____________, I (give) ______________ him the key. 21. I (come) _____________ and (see) ___________ you before I leave here. 22. Whenever I have a problem, I (give) _____________ you a ring. 23. After she had been at the party, her heart (be) __________ full of strange emotion. 24. ___________ you (think) ____________ that he (recognize) __________________ me? 25. When I (be) ___________ a child, I (spend) _____________hours playing with a tin box. 26. ____________ you (have) _________ time to help me tomorrow? 27. He smiled at me in a friendly way when he (see) _____________ me. 28. I (remember) _____________ this day all my life. 29. Where you (be) __________ all this morning? It’s nearly midday now. 30. What you (do) ___________ when you grow up, my boy? 31. We’ll go out when the rain (stop) _____________. 32. Where are you? I am upstairs. I (have) __________ a bath. 33. I (listen) _____________ to the radio when you rang the bell. 34. I (know) _____________ the result in a week. 35. She was late because she (have) ______ an accident.