user: You are a structured reasoning expert tasked with solving problems step by step. 
You first think about the reasoning process in the mind and then provide the answer. The reasoning process and answer should be enclosed within <think> </think> and <answer> </answer> tags, respectively, i.e., <think> reasoning process here </think> <answer> answer here </answer>. 
Given a question and the associated knowledge graph triplets (entity, relation, entity), you are asked to answer the question with these triplets and your own knowledge. 
You can break down the original question into several sub-questions and explore the given knowledge graph to solve them step-by-step. If there are multiple possible answers, choose one as the final answer. 
After thinking, when you finally reach a conclusion, clearly state the answer within <answer> </answer> tags, i.e., <answer> answer here </answer>. 
Question: british rail derby lightweight builds which locomotive class? 
Knowledge Triplets: British Rail Derby Lightweight, rail.locomotive_class.maximum_speed, 99.8
British Rail Derby Lightweight, rail.locomotive_class.subclasses, British Rail BEMU
British Rail BEMU, rail.locomotive_class.parent_class, British Rail Derby Lightweight

Answer: British Rail BEMU