Bán kính hình tròn B gấp 3 lần bán kính hình tròn A. Nếu hình A lăn xung quanh hình B, nó phải thực hiện bao nhiêu vòng quay để trở lại điểm xuất phát?

=> Các phương án được đưa ra là 3/2, 3, 6, 9/2, 9 vòng.

Giups em vs ạ 

Give the correct form of the verbs in parentheses:

1. Washing the dishes (be) ------------- the children’s job.
2. Each student in the class (have) ----- to have a book.
3. The number of students in this room now (be) --------------- twenty.
4. A number of students in the class (speak) ----------- English very well.
5. There (be) ----------- some interesting pictures in today’s paper.
6. Economics (be) -------- my favorite subject.
7. Ten minutes (be) ---------- more than enough time to complete this exercise.
8. Most people (like) ---------- to go to the zoo.
9. The police (be) ----------- coming. I’ve already called them.
10. Japanese (be) ----------- very difficult for English speakers to learn.
11. The old in my country (be) ---------- cared for by their children and grandchildren.
12. This exercise on singular-plural agreement of subjects and verbs (be) ---------- easy.
13. The subjects you will be studying in this course (be) ---------- listed in the syllabus.
14. Where (do) ---------- your parents  (live)............?
15. Some of the fruit in this bowl (be) --------- rotten.
16. The news about Mr. Hogan (be) ------------ surprising.
17. Twenty dollars (be) ---------- an unreasonable price for the necklace.
18. The English (be) ---------- proud, independent people.
19. Mumps usually (cause) ----------- a mild fever.
20. Knowledge of the fact (be) ------------ necessary to reach the wise decision.
21. The report of your grade (have) ---------- been in the office.
22. Three years (be) ----------- a long time without a job.
23. Tom and I (be) ----------- cousins.
24. Better methods of refrigeration (depend) --------- on engineers.
25. The export of rice, oil and coal (increase) ------------- since last year.
26. The police (want) ---------- to interview my friend about a robbery.
27. The United States (have) --------------- a population of around 250 million.
28. English (be) ------------- not my native language.
29. Neither Tom nor his friends (come) ------------- here.
30. None of the students (be) ------------- late yesterday.