I hope / we / able / solve the problems / over population and pollution.

• A. 
  I hope whether we are able to solve the problems, those are over population and pollution. 
• B. 
  I hope if we will be able to solve the problems, which are over population and pollution.
• C. 
  I hope that we will be able to solve the problems of over population and pollution.
• D. 
  I hope when we will be able to solve the problem for over population and pollution.