Table: coppa acerbo
Question: How many different drivers have competed in the Coppa Acerbo in 1940s?
Step 1 (Reasoning, Other Commonsense Reasoning): 1940s
Step 2 (Operation, Filter): year
Step 3 (Operation, Grouping): driver / s	
Step 4 (Reasoning, Aggregating): COUNT, driver / s
Answer: 4