| There are several reasons | | |
| Scientists are still uncertain about the exact cause | | |
| Building more roads has led | | |
| A better standard of teaching at primary school level has resulted | | |
| The high salaries available in more advanced economies has caused | | |
| Pollution will always be a problem because | | |
| Because | | |
| The rate of unemployment has fallen in some countries thanks | | |
| The rate of unemployment has risen in some sectors of the economy due | | |