Rewrite the sentences using the words given

rewrite the sentences using the words given    
1. lan has more old stamps than hoa. { fewer }
2. minh is the tallest boy in my class. { isn't }
3. mai has bought less milk than tom { more }
4. this is the first time i have come a big city. { never }
5. the city is too crowded for me to find him. { so }