Một đoạn ống thép dài 150m. Một học sinh dùng búa gõ vào một đầu ống thì một em khác đặt ở đầu kia của ống nghe được hai tiếng gõ. Tiếng nọ cách tiếng kia 0,415s a) giải thích vì sao tiếng gõ một tiếng mà đầu kia lại nghe được hai tiếng? b) tính vận tốc âm truyền trong không khí? Biết vận tốc truyền âm trong ống thép là 6000m/s

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Viết câu sao cho có nghĩa tương tự như câu gốc. 1,Mai used to type faster than she does now. -Mai doesn't type................................................ 2,The coffee is too hot for me to drink. -The coffee isn't....................................... 3,Trang hasn't written to her parents since May. -Trang last................................................................. 4,The distance from my house to school is about 500 metres. -It is................................................................................................... 5,My father went to work by cars some years ago,but now be goes by bus. -My father used..................................................................................................... 6,Don't drive too fast or you will have an accident. -If you............................................................................ 7,Is it possible to go to sapa by motorbike? -Can we...........................................................? 8,My mother is a careful driver. -My mother drives....................... 9,I found the film exciting. -I was................................... 10,It difficult for lan to pass the last exam. -Lan has.......................................................... 11,Hoa was tired,but she had to do all the house work. -Althouth Hoa....................................................................... 12,Despite the bad weather,the fooball match still happened. -Althouth the weather.................................................................... Mình cần gấp làm hết giúp mình với ạ, Cảm ơn nhìu.(mình sẽ vote nha).

I. Circle the best answer A, B, C or D to complete each sentence. 1. Choose the word that has the underlined part pronounced differently from the others A. buffalo B. photo C. limestone D. botanical 2. Choose the words that have the different stress from the others. A. affect B. billboard C. visual D. substance 3. Water…………………. in the lake has made the fish die. A. pollution B. pollute C. polluted D. polluting 4. If you can give me one good reason for your acting like this,………………………thisincident again. A. I will never mention B. I never mention C.will I never mention D. I don’t mention 5. Unless you ……………………… all of my questions, I can’t do anything to help you. A. answered B. answer C.would answer D. are answering 6.If someone………………into the store, smile and say, “May I help you?” A. comes B.came C.come D. should come 7. “Here’s my phone number”. “Thanks. I’ll give you a call if I……………………some help tomorrow” A. will need B. need C.would need D. needed 8.If I didn’t work for an accounting firm, I…………………in a bank now. A. work B.will work C. have worked D. would work 9.Too much use of.......................lights in cities may cause light pollution. A. traffic B. aquatic C. sigh D. electric 10. If the factory continues ………………… poison into the lake, all the fish and other aquatic animals will die. A. dumped B. to dump C. dump D. dumping 11.If she…………………him, she would be very happy. A. would meet B. will meet C. met D. should meet 12. If I had enough money, I…………….abroad to improve my English. A. will go B. would go C. went D. should have go to 13.Households dump waste ...............the river, so it is polluted A. down B. on C. in D. into 14. Students are more aware .................protecting the environment. A. to B. in C. of D. with 15. .......................from households is another cause leads to water pollution. A. Sewage B. Herbicides C. radioactive D. thermal B. WRITING I. Rewrite the following sentences, using the words in brackets. 1. Dumping solid wastes in rivers, lakes and oceans causes water pollution. (result in) →…………………………………………………………………………………………………………….. 2. Global warming makes water temperature go up. [due to) →Water temperature……………………………………………………………………………………. II. Rewrite the following sentences, using conditional sentences Type 1 or 2 1.People throw rubbish in the street.The street doesn’t look attractive. →…………………………………………………………………………………………………………….. I’ll probably get lost unless he comes with me. →……………………………………………………………………………………………………………..