Gọi 3 số đó là a; a+1; a+2. Ta có:

a + (a+1) + (a+2)

= a+a+a+1+2

= 3a +3 

= 3(a+1) chia hết cho 3

=> Tổng 3 số tự nhiên liên tiếp chia hết cho 3 (Đpcm)

Gọi 4 số đó là n; n+1; n+2; n+3. Ta có:

n + (n+1) + (n+2) + (n+3)

= n+n+n+n+1+2+3

= 4n +6

Vì 4n chia hết cho 4 mà 6 chia 4 dư 2

=> 4n+6 chia 4 dư 2

=> Tổng 4 số tự nhiên liên tiếp không chia hết cho 4 (Đpcm)

Cho hỗn hợp gồm Na và Al có tỉ lệ số mol tương ứng là 1:2 vào nước (dư). Sau khi các phản ứng xảy ra hoàn toàn, thu được 8,96 lít khí H₂ (ở đktc) và m gam chất rắn không tan. Giá trị của m là

A. 7,8

B. 5,4

C. 43,2

D. 10,8

1. collection

2. sporty

1. Would you like to go for a walk in the park this afternoon? (for-at/for-in/to-at)

2. My children are important to me. (for/to/with/by)

3. He is different from his brother (from/between/to/with)

4. My sister is interested in reading novels (at/to/in/with)

5. This car belongs with my mother (with/in/on/to)

6. She likes going for a picnic on foot. (for-in/for-on/to-by/to-on)

7. Mary is fond (to/with/about/of) music.

25 Many pupils are bad at English. (at/in/for/with)

8. I came on Monday at 10 o'clock in .the morning. (in-at-in/on-in-at/on-at-in)

9. He walked into the room on which we were sitting (in-in/into-in/into-on/in-on)

10. We were classmates. She sat next to me . (beside/next to/in/on)

11. It is necessary to learn English now. (for/to/in/with)

12. Eating a lot of fruits is good for your health. (to/with/in/for)

13. Dalat is famous for flowers (to/for/with/by)

14. She only likes sitting by a fire in winter. (in-in/on-in/by-in/by-on)

15. My son is good at all sports,but he is bad .at cooking. (at-in/in-at/at-at/with-at)

16. Wine is made from grapes. (to/with/in/from)

35.This table is made from wood.(from/of/in/to)

17. I don't agree with you at all about that. (to/with/for/of)

18. I like to go for holiday on the beach in summer. (to-on-in/in-on-on/for-on-in)

19. Wait for me in a few minutes.I'm busy at the momemt . (to-in-at/for-in-at/of-for-in/for-for-at)

20. I paid $ 5 for this books (to/for/bu/with)

21. I shall meet you at the corner on the street.

22. It never snows at Christmas

23. My birthday is in May 5 th

24. He always goes on time for the class.

25. Please write your name on the top of the page.

26. The room was full of. people

27. I would like to be independent of everyone

28. I'm tired of waiting for her

29. This country is rich in oil

30. My cat is fond of fish

31. Elvis Presley grew in poor home

32. He had fallen in love with her when they were in school

33. Children like swimming in the water in summer

34. She isn't in the room. She is in the garden

35.He was standing in the middle of the room when I came

36. We get a lot of rain in November

37. I can't see you on Monday,I can see you at weekends

x \(\in\){ 45;60 }

1. Hue / Mr Nam / to night / arriving / in / is.

=> Mr Nam is arriving in Hue tonight.

2. back / in / months / going / England / they / two / are / to.

=> They are going to back in England two months,

3. It / not / difficult / is / this sentence / to / translate / into / English.

=> It is not difficult to translate this sentence into English.

4. Would / lending / you / me / mind / dictionary / your ?

=> Would you mind me lending your dictionary?

5. think / I / do / speaking / you / should / every / practice / day

=> Do you think I should practice speaking every day?

6. English / will / best / I / to / try / improve / my / my.

=> I will try my best to improve my English.

7. much / per / time / cooking / how / you / spend / do / day?

=> How much time per day do you spend cooking?

8. difficult / it / not / to / English / think / is / learn / I.

=> I thinkit is not difficult to learn English.

9. She / speaker / good / is / English / a.

=> She is a good Ebglish speaker.

10. are / to / where / going / you / hometown / your ?

=> where are you going to your hometown?

Khi đốt cháy hoàn toàn một polime X chỉ thu được CO₂ và hơi nước với tỉ lệ số mol tương ứng là 1 : 1. X có thể là polime nào dưới đây

A. Polipropilen

B. Tinh bột

C. Polistiren

D. Poli(vinyl clorua)

1. B.never

2. C.with

3. C.better