Final answer:
The polar jet stream flows from west to east between the polar cell and the Ferrel cell, functioning as an upper-air wind influenced by Earth's rotation and temperature gradients. So the correct option is B.
Step-by-step explanation:
The sentence that correctly describes the polar jet stream is: It flows from west to east between the polar cell and the Ferrel cell. The jet stream is a powerful upper-air wind circulating in a west-to-east direction due to the rotation of the Earth and temperature variations between the equator and the poles. The polar jet stream specifically operates between the polar and Ferrel cells, which are part of the Earth's atmospheric circulation system.