Correct answer is C. Utilizing broadcast variables to minimize data transfer across nodes during join operations. Explanation: Data shuffling, a common performance bottleneck in Apache Spark, involves moving data across cluster nodes, which can significantly slow down job performance. Broadcast variables offer an efficient solution by distributing read-only data to all nodes, thereby reducing the need for data shuffling during join operations. While increasing executor size and core count can enhance processing speed, it doesn't directly tackle shuffling issues. Similarly, using efficient serialization formats like Parquet improves performance but doesn't specifically address shuffling. Custom partitioners can optimize performance by evenly distributing data, but they may not be as straightforward or effective as broadcast variables in minimizing data transfer during joins. Thus, broadcast variables stand out as a targeted strategy for reducing data shuffling and optimizing Spark job performance in Databricks.