Một phân tử ADN có chiều dài 17x106A0 và số nucleotit loại A chiếm 30% tổng số nucleotit. Phân tử ADN này nhân đôi liên tiếp 3 lần liên tiếp. Hãy xác định: a) Số nucleotit mỗi loại của phân tử ADN. b) Số phân tử ADN được tạo ra. c) Số nucleotit mỗi loại mà môi trường cung cấp cho quá trình nhân đôi. d) Số phân tử ADN được cấu tạo hoàn toàn từ nguyên liệu môi trường.

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1/ She _________ the house last weekend. * A. was cleaning B. cleans C. clean D. cleaned 2. I _________ a little English before I went to Singapore. * A. study B. had studied C. had study D. have studied 3/ Why _________ you absent yesterday ? * A. did B. are C. was D. were A. meet B. met C. did meet D. were meet 5/ When he _________ , she was cleaning her room. * A. arrives B. arrived C. is arriving D. was arriving 6/ Last night, the police _________ me on my way home. * A. is stopping B. stopped C. stops D. was stopping 7/ Mai and Huong _________ their last summer vacation on the farm. * A. don’t spend B. aren’t spent C. didn’t spend D. weren’t spent 8/ What _________ you _________ last night? * A. do / do B. did / do C. do / did D. were / doing 9/ Before I went to bed, I _________ my teeth. * A. have brushed B. had brushed C. brushed D. brush 10/ The floor _________ with a sheet of plastic five days ago. * A. covered B. was covering C. was covered D. is covered 11/ Before my mother came home, my brother _________ food on the table. * A. had prepared B. have prepared C. prepared D. had prepare 12/ Phong _________ with his friends last month. * A. went fish B. went fished C. went fishing D. went to fish 13/ I watched movie after I _________ my homework. * A. have completed B. had complete C. had completed D. completed 14/ She _________ breakfast at 8.30 yesterday morning. * A. had B. is having C. was having D. has 15/ When I got up, it _________. * A. rains B. rained C. is raining D. was raining 16/ Mrs. Thu _________ the newspaper while her husband was watching T.V. * A. was reading B. is reading C. reads D. read 17/ Mr. Quang fell over while he _________ basketball. * A. was playing B. is playing C. played D. plays 18/ When I came home, everybody _________ the television. * A. watched B. were watching C. was watching D. is watching 19/ My father _________ out when my sister arrived at the zoo . * A. goes B. have gone C. has gone D. had gone 20/ Alice _________ a Vietnamese person until he met Nam. * A. had never met B. have never met C. never met D. never have met mình cần gấp nha thank