The Spectrum of a Very Distant Star Shows Spectral Absorption

Multiple Choice

The spectrum of a very distant star shows spectral absorption lines of ionized helium,He II,and molecular absorption bands from titanium oxide,TiO.What could you conclude about this star?

A) The star is probably the spectrum of a binary system, two stars close together, a hot star and a cooler companion, unresolved as separate stars from Earth but contributing separate spectra.
B) The star must have a very hot atmosphere containing helium gas overlying a much cooler stellar surface.
C) The star must have a thick, cool atmosphere overlying a hot stellar atmosphere.
D) There must be cool, interstellar gas containing TiO between the star and Earth.