nhanh thế 

79.There're lots of work to do for us.

80.Number of your children is six.

66. How much do the two notebooks cost?

67. Phong is Nhung's younger brother

69. Are there over eight hundred students in your school?

70. That is Mr. Trung's motorbike

câu 68,71 thì OK

18. Mary is Peter's sister.

19 đúng rồi

20. John is Mr. and Mrs. Black's son.

21. Mr Ba gets to work by motorbike everyday.

22. There are six hundred students in my school.

23. Jack is Julia's brother.

36 His house is to the right of the book store

37 It's a tall building

38 Tom goes to work by car every morning

39 How much meat would you like

40 There are 20 packets of tea in this box

41 How much do 2 notebooks cost?

43 He go to work at a quater past seven

44 Are there over 800 students in your school?

45 That is Mr Trung's motorbike

48 Are there 25 students in your class

49 He goes to work at a quater past seven

1 to listen

2 they are

3 because

4 drink

5 pleasant

6 doesn't he

nKClO3= 49/122,5=0,4(mol)

a) PTHH: 2 KClO3 -to-> 2 KCl + 3 O2

b) nO2=3/2 . nKClO3= 3/2 . 0,4= 0,6(mol)

=> V(O2,dktc)=0,6 x 22,4= 13,44 (l)