A Star of Twice the Mass of the Sun Reaches

A star of twice the mass of the Sun reaches the asymptotic giant branch (AGB) phase of its life and begins to eject large amounts of carbon and heavier elements into space. What process occurs to make this component easy to detect, particularly at radio wavelengths?

A) The carbon grains (soot!) are heated by radiation and reemit a cool thermal continuum spectrum whose peak is at radio wavelengths.
B) The carbon nuclei acquire electrons and become neutral atoms in an excited state, which then emit an easily detected spectrum as they de-excite.
C) Carbon and oxygen nuclei have such high velocities that they undergo nuclear fusion in a shell surrounding the star to produce heavier elements whose emissions are at radio wavelengths.
D) Carbon and oxygen combine chemically to produce the easily detected CO molecule.