Final answer:
Heterotrophs depend on producers and autotrophs for survival as they cannot produce their own food. Autotrophs are essential in converting solar energy into chemical energy, which sustains the food chain.
Step-by-step explanation:
Heterotrophs, or consumers, cannot produce their own food and therefore rely on other organisms for their energy and carbon needs. They obtain energy by consuming producers (autotrophs) like plants, algae, and some bacteria that synthesise their own food through photosynthesis. In essence, heterotrophs cannot live without autotrophs that convert solar energy into chemical energy, which is then passed up the food chain.
Humans are an example of heterotrophs, specifically omnivores, that depend on both producers and other animals for sustenance. Without autotrophs, the food chain would collapse and all heterotrophic organisms would eventually perish. Thus, the correct response to the question of what heterotrophs could not live without is 'd. A and C'.