Answer: drop()

The `drop()` method is used to remove duplicate columns from a DataFrame after an inner join. Here's why the other options are not suitable: - `drop_duplicates()` and `dropDuplicates()` are used for removing duplicate rows, not columns. - `dropColumns()` and `dropDuplicateColumns()` are not valid methods in Spark. For more details, refer to the Spark documentation on the `drop()` method.

Author: LeetQuiz Editorial Team