1 This question is diffcult to understand 

-> It's 

2 Travel around Ha long Bay is very interesting 

-> It's 

3 They collect used cans and bottles for recycling 

-> Used cans 

4  The car is very expensive. It is made in japan 

-> The car 

5 Going fishing with friends at weekends is interesting 

-> It's 

6 The woman is sitting at the first desk. She is the secretary 

-> the woman sitting