II.

1. My school has donated books for street children for 2 years .

2. They cleaned up their streets yesterday .

3. I have visited Hue four times .

4. She didn’t watch TV yesterday .

III, 

WRITING-I

1.will be used in the future.

2. she lives far from school, she always go to school early.

3.been playing chess for 5 years.

4.of his sickness, he goes to school.

1 B

2 D

3 C

4 D

5 C

6 B

7 B

8 B

9 B

10 B

11 A

12 C

13 C

14 C

15 C

16 D

17 A

18 A

raining đổi thành rains

raining➞rains

a) \(K^I_x\left(CO_3\right)^{II}_y\)

Theo quy tắc hóa trị: x.I = y.II

=> \(\dfrac{x}{y}=\dfrac{II}{I}=\dfrac{2}{1}\)

=> K₂CO₃

b) \(Fe^{III}_xO_y^{II}\)

Theo quy tắc hóa trị: x.III = y.II

=> \(\dfrac{x}{y}=\dfrac{II}{III}=\dfrac{2}{3}\)

=> Fe₂O₃

c) \(Al^{III}_x\left(SO_4\right)^{II}_y\)

Theo quy tắc hóa trị: x.III = y.II

=> \(\dfrac{x}{y}=\dfrac{II}{III}=\dfrac{2}{3}\)

=> Al₂(SO₄)₃

d) \(H^I_xS^{II}_y\)

Theo quy tắc hóa trị: x.I = y.II

=> \(\dfrac{x}{y}=\dfrac{II}{I}=\dfrac{2}{1}\)

=> H₂S

K2CO3 (98)

Fe2O3 (160)

Al2(SO4)3 (342)

H2S (34)