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: what rail network does willunga railway line belong to? 
Knowledge Triplets: Northfield railway line, rail.railway.part_of_network, TransAdelaide
TransAdelaide, rail.rail_network.railways, Henley Beach railway line
Seaford railway line, rail.railway.part_of_network, TransAdelaide
TransAdelaide, rail.railway_operator.railways, m.05yrjyz
Willunga railway line, rail.rail_network.railways, TransAdelaide
TransAdelaide, rail.rail_network.railways, Grange railway line
Grange railway line, rail.railway.part_of_network, TransAdelaide
TransAdelaide, rail.rail_network.railways, Semaphore railway line
TransAdelaide, rail.rail_network.railways, Tonsley railway line
Public transport, business.industry.companies, TransAdelaide
TransAdelaide, rail.rail_network.railways, Belair railway line
Henley Beach railway line, rail.railway.part_of_network, TransAdelaide
Tonsley railway line, rail.railway.part_of_network, TransAdelaide
Outer Harbor railway line, rail.railway.part_of_network, TransAdelaide
TransAdelaide, rail.rail_network.railways, Seaford railway line
m.05yrjyz, rail.railway_operator_relationship.operator, TransAdelaide
TransAdelaide, organization.organization.date_founded, 1994-07
TransAdelaide, rail.rail_network.railways, Outer Harbor railway line
Semaphore railway line, rail.railway.part_of_network, TransAdelaide
TransAdelaide, rail.rail_network.railways, Penfield railway line
TransAdelaide, rail.rail_network.railways, Northfield railway line
Willunga railway line, rail.railway.part_of_network, TransAdelaide
Belair railway line, rail.railway.part_of_network, TransAdelaide
Penfield railway line, rail.railway.part_of_network, TransAdelaide
TransAdelaide, organization.organization.headquarters, m.062tp3r
TransAdelaide, business.business_operation.industry, Public transport
TransAdelaide, rail.rail_network.railways, Gawler Central railway line
TransAdelaide, rail.rail_network.railways, Willunga railway line
Gawler Central railway line, rail.railway.part_of_network, TransAdelaide

Answer: TransAdelaide