Describe desert encroachment under the following headings

(a) causes (b) areas liable (c) effect (d) methods of prevention 
 

 (a) Using specific examples, describe any three causes of air pollution

(b) Outline three major effects of air pollution 

(c) Suggest any three ways of controlling air pollution 

(a) Explain any four factors that-determine population distribution

(b) Describe any two types of population movement

(c) What four problems are associated with any one of the types of population movement described in (b) 
 

(a) In what four ways does a town differ from a village?

(b) Describe with examples three functions which a town may perform for a village 
 

Using specific examples, discuss rail transportation in African countries under the following headings

(a) Reasons for construction (b) Problems (c) Solutions