The correct answer is D because defining an individual file format is a Snowflake best practice for data unloading, especially when regularly unloading specific data types. This approach ensures consistent file characteristics and simplifies the unloading process. Option A is incorrect because SINGLE = TRUE is not recommended for larger files as it can cause performance issues; instead, Snowflake recommends allowing multiple files for better parallelism. Option B is incorrect because OBJECT_CONSTRUCT(*) is not specifically tied to Parquet format usage and is not a general unloading best practice. Option C is incorrect because avoiding CAST functions is not a recommended practice; CAST functions are often necessary for data type conversions during unloading.