Table: joakim bonnier
Question: Which chassis and engine combination was used by Joakim Bonnier the most during his career?
Step 1 (Operation, Indexing): chassis
Step 2 (Operation, Indexing): engine
Step 3 (Reasoning, Aggregating): COUNT, chassis and engine combination
Step 4 (Reasoning, Other Commonsense Reasoning): the most
Answer: maserati 250f and maserati straight - 6