Final answer:
The energy input into an ecosystem primarily comes from sunlight and chemical compounds. Sunlight is utilized by plants and certain microbes through photosynthesis, while ecosystems like hydrothermal vents rely on chemicals for energy. The correct option is a and b.
Step-by-step explanation:
The energy input into an ecosystem can come from sunlight and chemical compounds. Sunlight is a primary source of energy for most ecosystems, and many organisms, like plants and certain microbes, use this energy through the process of photosynthesis to convert CO2 and water into organic compounds and release oxygen. In contrast, some ecosystems, particularly those without access to sunlight like hydrothermal vents, rely on chemical compounds for energy. These ecosystems utilize chemicals such as hydrogen sulfide to derive energy. Hence, the correct answers to the question are a. sunlight and b. chemical compounds, making option d. 'A and B' the correct choice.