--> The last time he enjoyed his holiday in Da Lat was in 2000.
--> He has not enjoyed his holiday in Da Lat since 2000.

a)Theo đề bài,
P+E+N=25 mà P=E => 2P+N=25 (1)
2P-N=7 (2)
Từ (1) và (2) --> N=\(\dfrac{25-7}{2}\)=9
                     --> 2P=9+7=16 => P=E=16/2=8
Vậy N=9, P=E=8
b) A có 8 P --> A là Oxi
CTHH của hợp chất đó là FexOy (x,y∈N*) (Fe hóa trị III)
Theo quy tắc hóa trị:
III.x=2.y ---> x/y=2/3
--> CTHH của hợp chất là Fe2O3

We can't see the star at night because there is too much light pollution.
I decided to go home because the film was boring.

1, shouldn't
2. musn't
3. can
4. should

1. were visited
2. bore
3. was built
4. was not produced
5. were not hidden 

1. Why didn't you come to Hoa's birthday party last Monday?
2. We and he have been close friends since we were in primary school.

1. is planting
2. saw
3. to finish
4. will go
5. performed
6. add
7. taught

1. A
2. B
3. C
4. C
5. A
6. C

She told us to shut the door but not to lock it because she would be back soon.