Fact 1: High pressure systems cause clear weather.

Fact 2: Sailplanes fly in clear weather.

Given the two facts above, answer the question "What do high pressure systems allow?" with the following options: 
- water conservation
 - Veins and arteries.
 - hydrogen and oxygen
 - Animal survival
 - to move people
 - heat energy
 - heating liquids
 - sailplanes to fly


 

        sailplanes to fly 