Because, photoautotrophs serves as their carbon sources.
Chemoheterotrophic bacteria are those bacteria that are incapable of producing their own food, they depend on photoautotrophs, which are capable of making their own food by trapping energy from the sun. Thus, photoautotrophs serves as source of food for the chemoheterotrophic bacteria.
D is what he probably thought but it all depends on genetics so if they did stretch out the kid would still have a short neck to it would be A
