Which Is the Best Description of the Mutual Benefit to Both

Which is the best description of the mutual benefit to both species found in a lichen?

A) The autotroph provides energy and the heterotroph prevents dehydration
B) The autotroph prevents dehydration and the heterotroph provides energy
C) The autotroph produces oxygen and the heterotroph consumes oxygen
D) The heterotroph protects the autotroph from predation
E) The autotroph produces antibiotics to ward off infection by bacteria