Đèn ống phát sáng là do đâu? Đèn LED chỉ phát sáng khi nào?

Cho hệ phương trình: $\left \{ {{xy/x+y=1/7} \atop {xy/3y+8x=1/46}} \right.$ Nghiệm của hệ trên là: x=....., y=.......

Tập tính nào ở chim có mà bò sát không có?

ai giúp bài 1,3 vbt bài nhân hóa trang 43-44 vs ạ em cảm ơn ạ

7 tb sinh giao tử có kiểu gen AaBbDd thực hiện quá trình giảm phân tạo giao tử . biết ko xảy ra đột biến . số loại giao tử tối da là

so sánh và cho biết điểm giống nhau trong hoạt động kinh tế của ba nuóc Lào ,Việt nam , campuchia ? giúp mình vói

We were late for school because of the heavy rian

helpppppppppppppppppppppppppppppppppppppp

1. You took tired. (you/study) hard? 2. Mr. Brown is new here, isn’t he? How long (he/work) for the company? 3. I (lose) my wallet. Have you seen it anywhere? 4. I (read) the magazine you lent me, but I (not/finish) yet. 5. (you/hear) the bad news? Simon (break) his leg! 6. John (write) his novel since last year. He the first three chapters. 7. What (you/do) ? I (wait) for you for an hour. 8. The painters (paint) the town hall since February. They (paint) nearly half of it now. 9. I (know) Louise for ten years. 10. Mr. Brown (mark) the exams all morning, but he (not/read) them all. Exercise 4: Choose the best option to complete the sentence. 1. She can’t come to the phone now because she ...... tomorrow’s test. A. studies B. is studying C. has studied D. has been studying 2. They must be at the sports ground now. They usually .............. basketball on Fridays. A. play B. are playing C. have played D. have been playing 3. I ..................... my work already. I’m ready to go for a walk with you. A. finish B. am finishing C. have finished D. have been finishing 4. I ..................... breakfast right now. Can you call a tittle later? A. cook B. am cooking C. have cooked D. have been cooking 5. I ..................... this book. Can I borrow it tor a week or so? A. don’t read B. am not reading C. haven’t read. D. haven’t been reading Huyền

giup mik moi nguoi!!!! Mik cam on