Bipolar Outflows Create Bright Bow Shocks Because

Multiple Choice

Bipolar outflows create bright bow shocks because

A) the gas "piles up" when it encounters ultraviolet light.
B) the material collides with particles in the interstellar medium.
C) the star's magnetic fields trap the outflow material there.
D) the gas cools enough to allow H ^- ions to build up.
E) the outflows encounter newly forming planets.