Given the task definition and input, reply with output. In this task, you need to answer basic science questions. For each question, several terms are intentionally masked with ***. This masking can cover very few or many of the question words. Clearly, if masked terms are important, the modified question will be impossible to answer. Please indicate the correct answer with one of the following responses: "A", "B", "C", "D" or "E". While "A"-"D" correspond to the answer options provided in the input, "E" represents "I don't know" for questions that do not provide enough information. Respond via "E" if the question is not answerable. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D', 'E'.

Question: Diatoms are microorganisms that produce sugars through the process of photosynthesis. Diatoms are an example of a *** that is __________.  (A) visible to the naked eye (B) disease-causing in humans (C) a primary producer (D) responsible for decompositio.

C.