You are presented with the quiz "What enters ecosystems?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "energy enters ecosystems in the form of sunlight or chemical compounds" and "solar energy is clean energy ". So, what's the best answer to the question?

Available choices: a. an object; b. Waste; c. bacteria; d. Solar light; e. heat produced; f. Plastics; g. Metals; h. rays or beams;
The answer is:
d.