`5` Her younger sister is not as beautiful as her.

`-` So sánh bằng phủ định: S1 + be + not as + adj + as + S2

`6` They began studying English in `2004`.

`-` S + begin + V-ing: bắt đầu làm gì

`7` I used to collect stamps when I was in primary school.

`-` S + used + to V: đã từng làm gì

5. Her younger sister isn't as beautiful as her.

S + be (not) + as +ADJ + as + O : so sánh bằng 

6. They began studying English in 2004.

S + has/have + V3/ed + for/since + time 

--> S + started / began + to V / Ving 

--> It is / has been + time + since + S+ V2/ed 

7. I used to collect stamps when I was in primary school.

used to + V1: đã từng (không còn ở hiện tại)

`color{orange}{~LeAiFuRuiHuiBao~}`