Energy in most ecosystems must flow through autotrophs because

Energy must flow through autotrophs because they take the energy from the sun, then herbivores feed off the autotrophs converting energy from the plant into energy that they can use. Carnivores then feed off the herbivores, and finally carnivores feed off of each other, and the process starts over again. Heterotrophs only generate a small fraction of their energy through photosynthesis, making autotrophs very important. 

Ithink all of these events

The correct answer is "b"