original_query: What was the cause of Attilio Bettega's fatal crash during the Tour de Corse? What is the most relevant chunk to answer the query?
query: What was the cause of Attilio Bettega's fatal crash during the Tour de Corse?
answer: The provided text states that Attilio Bettega crashed fatally during the fourth special stage at the Tour de Corse, but it does not specify the cause of the crash.