Fog, the other three options would be too high in the atmosphere to cause visibility problems.
Answer:
1868 years
Explanation:
The Persians lost against the Greeks in 479 BCE (which stands for Before Common Era or Before Christ). On the other hand, the Serbs were conquered by the Turks in 1389 CE (Common, modern Era).
All of the colonies except Cuba and Puerto Rico attained independence by the 1820's.