1 English,which is spoken around the world, is the language used in aviation

2 Although he works very hard , he didn't feel tired 

3 The Sword Lake ,which water is always blue , is in HN

4 Do you know the woman whose they are talking 

5. English is(the language used in aviation It is spoken around the world..(relative clause)
⇒ English, which is spoken around the world, is the language used in aviation.
6. He worked very hard, but he didn't feel tired. (Although)
⇒ Although he works very hard, he didn't feel tired.
7. Sword Lake is in Ha Noi. The water of it is always blue. (relative clause)
⇒ The Sword Lake, which water is always blue, is in Ha Noi.
8. Do you know the woman? They are talking about that woman. (relative clause)
⇒ Do you know the woman whose they are talking?