Fact 1: High pressure systems cause clear weather.

Fact 2: During windy weather, the pollution is dispersed and cleared away.

Given the two facts above, answer the question "What cause pollution to disperse?" with the following options: 
- low pressure systems
 - fissures of hot, acidic water
 - zero pressure systems
 - fossil fuels
 - harmful substances
 - no pressure systems
 - high pressure systems
 - Greenhouse gases


 

       high pressure systems  