The correct answer is B (PATTERN) because the Snowflake documentation explicitly states that using the PATTERN parameter to filter on a large number of files can negatively impact performance. The community discussion shows 100% consensus on answer B, with multiple comments referencing the official Snowflake documentation that advises avoiding patterns that filter on large file sets for optimal performance. While other parameters like FILE_FORMAT, VALIDATION_MODE, and FILES are also optional COPY INTO parameters, they don't have the same documented performance implications when dealing with large numbers of files as the PATTERN parameter does.