Answer: DataFrame.join()

Wide transformations in Apache Spark require data shuffling across partitions. Among the options, DataFrame.join() (B) is classified as a wide transformation because it often requires shuffling data to align matching keys across partitions. The other operations, DataFrame.filter() (A), DataFrame.select() (C), DataFrame.drop() (D), and DataFrame.union() (E), are considered narrow transformations as they do not require data shuffling across partitions.

Author: LeetQuiz Editorial Team