You are presented with the question "What causes good visibility?" and the following answer choices: 
- permineralization
 - focusing a lens
 - high pressure systems
 - flashlights
 - peachleaf willow
 - the Great Barrier Reef
 - an electron microscope
 - windpower operated machines

Now knowing that high pressure systems cause clear weather and weather Clear weather usually means good visibility, choose the best answer.


 

   high pressure systems      