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: Electromagnets are used in many electric motors, generators, and simple devices. Electromagnets are much more useful than permanent magnets *** unlike permanent magnets, electromagnets __________.  (A) come in a variety of sizes (B) have an attractive force (C) have two magnetic poles (D) can be turned on or of.
D.