There are many problems the world's cities ought to be resolved, nevertheless, the increasing number of waste disposal and not enough space of housing should be the most important issues.
As you know, nowadays, there are more and more people living in the urban area. Some of them moved from the rural area because of many reasons, such as to improve their quality of life. It makes the growth of people in the city, as a result, the city has become overcrowded. In order to solve this problem, the government can start to develop the countryside, consequently, people need not to move to the city. In addition, while developing the rural area, more job opportunities will be produced and it can attract people with knowledge to stay and teach the local people.
For the second problem, the increasing number of waste disposal, raise because of the economic growth of cities, especially in developed cities. As the city has become more prosperity, people spell more for their needs. The amount and the beauty of packing increased compared with the old days. Most like, those packing are made with plastics and it takes a thousand years in order for a plastics to biodegrade, reported by many Universities. Reduce, reuse and recycle are things we have to do to solve the problem of waste disposal. The first step is not to buy things we do not need. If the item is really needed, try to reuse it until it cannot be used. Last but not least, try to recycle those biodegradable parts to reduce wastes production.
To conclude, governments can develop countryside in order to help resolving the housing problem. For the disposing of wastes, three theories we have to follow, reduce, reuse and recycle. With these solutions, the key problems in the world's cities nowadays could be resolved. 
There are  
many
  problems
 the world's  
cities
 ought to  
be resolved
,  
nevertheless
, the increasing number of  
waste
 disposal and not  
enough
 space of housing should be the most  
important
 issues.
As you know, nowadays, there are more and more  
people
 living in the urban area.  
Some
 of them  
moved
 from the rural area  
because
 of  
many
 reasons, such as to  
improve
 their quality of life. It  
makes
 the growth of  
people
 in the city,  
as a result
, the city has become overcrowded. In order to solve this  
problem
, the  
government
 can  
start
 to develop the countryside,  
consequently
,  
people
 need not to  
move
 to the city.  
In addition
, while developing the rural area, more job opportunities will be  
produced and
 it can attract  
people
 with knowledge to stay and teach the local  
people
.
For the second  
problem
, the increasing number of  
waste
 disposal, raise  
because
 of the economic growth of  
cities
,  
especially
 in developed  
cities
. As the city has become more prosperity,  
people
 spell more for their needs. The amount and the beauty of packing increased compared with the  
old
 days. Most like, those packing  
are made
 with  
plastics and
 it takes a thousand years in order for  
a plastics
 to biodegrade, reported by  
many
 Universities.  
Reduce
, reuse and recycle are things we  
have to
 do to solve the  
problem
 of  
waste
 disposal. The  
first
 step is not to  
buy
 things we do not need. If the item is  
really
 needed, try to reuse it until it cannot be  
used
. Last  
but
 not least, try to recycle those biodegradable parts to  
reduce
  wastes
 production. 
To conclude
,  
governments
 can develop countryside in order to  
help
  resolving
 the housing  
problem
. For the disposing of  
wastes
, three theories we  
have to
 follow,  
reduce
, reuse and recycle. With these solutions, the key  
problems
 in the world's  
cities
 nowadays could  
be resolved
.