1.in 2050, the world's population will grown to 9 billion
->in 2050, the world's population will grow to 9 billion
2.traffic congestion has become a serious problem in big cities, doesn't it?
->traffic congestion has become a serious problem in big city , doesn't it?
3.the amount of motorbikes should be limited to reduce traffic jams
->the amount of motorbikes should be limited to reduce  congestion
4.nearly one million people live in dharavi , the largest slum of Mumbai 
->near one million people live in dharavi , the largest slum of Mumbai 
5.forest areas are destroy to make space for new house
->forest areas are destroyed to make space for new house
6. less than thirty children each year develop the disease
-> less than thirty children each year have developed the disease 
7. there are social causes of homeless , such as a lack of housing ,poverty and unemployment
->there are social causes of homeless , such as the lack of housing ,poverty and unemployment
8.your father used to drink coffee every morning,usedn't he
->your father used to drink coffee every morning,didn't he