What causes polar jet streams to form?

A. High-pressure systems
B. Rapid changes in wind direction
C. Air masses moving away from each other
D. Warm and cold air masses

3 answers

From Internet:

Undercutting sub-tropical air masses by polar air masses leads to the formation of polar jet streams. 2 This leads to surface low pressure and altitude high pressure.
soooo
whats the answer
It's D. Warm and cold air masses