1.It's necessary for the government to find a solution to reduce traffic jams. [ have ] 
=> The government have to find a solution to reduce traffic jams.
2.What is the population of Ho Chi Minh City? [in ] 
=> How many people living in HCM city?
3.They no longer love going out at the weekend, don't they ? [used ] 
=> They used to love going out at the weekend, didn't they?
4.there is more crime in cities than in rural areas [ lower]
=> Crime rates in rural areas are lower than those in cities 
5.Most people think overpopulation is less dangerous than it is [more]
=> Overpopulation is more dangerous than most people think of it.
6.Although the weather was bad , I had a very good time in Brazil [ spite]
=> In spite of the bad weather, I had a very good time in Brazil.
7.Crime affects everyone in different ways [ by]
=> Everyone is affected by crime in different ways.
8.You want to have a look at my new car , don't you? [ like ] 
=> You'd like to have a look at my new car, wouldn't you?