The Term "Baryon Cycle," as Astronomers Use It, Refers To

The term "baryon cycle," as astronomers use it, refers to:

A) the steps in the fusion of hydrogen into helium at the center of stars
B) the kinds of orbits short-period comets take around the Sun
C) the movement of interstellar material into the Galaxy and into stars and then the movement out when stars end their lives
D) the change of individual atoms into molecules in dusty interstellar clouds
E) exercise equipment they had in the White House for President Obama