`4.` My best friend loves to go to Seoul where the street food is very delicious.

- Relative Adverb (Trạng từ quan hệ)

- Where đại diện cho nơi chốn

- ... + N(place) + where + S + V + ...

`5.` The scientific research of  Stephen Hawkins  who is an English physicist has contributed a lot to humankind 

- Relative Pronouns (Đại từ quan hệ)

- Who thay thế cho danh từ chỉ người

- ... + N(person) + who + V + O

`6.` My most favorite item of clothing is the blue T-shirt which my mother bought for me.

- Relative Pronouns (Đại từ quan hệ)

- Which thay thế cho danh từ chỉ vật

- ... + N(thing) + which + S + V / V + ...

4. My best friend loves to go to Seoul. The street food here is very delicious.

-> my best friend loves to go to Seoul where the street food is very delicious

-> cấu trúc trạng từ quan hệ where : place + where + S + V

-> dùng where thay thế cho địa điểm

5 Stephen Hawking’s scientific research has contributed a lot to humankind. Stephen Hawking is an English physicist.

-> the scientific research of  stephen hawkins  who is an English physicist has contributed a lot to humankind 

-> cấu trúc mệnh đề quan hệ who : person + who + v + o 

-> dùng who thay thê scho ng

6 My most favorite item of clothing is the blue T-shirt. My mother bought it for me.

->  my most favorite item of clothing is the blue T-shirt which my mother bought for me

->  my most favorite item of clothing is the blue T-shirt that my mother bought for me

-> cấu trúc mệnh đề quen hệ which : 

-> C1 thing + which + s + v 

-> C1 thing + that + s + v