Answer: DataFrame.join()

In Apache Spark, the `DataFrame.join()` method is the correct way to perform a left join by specifying the `how` parameter as "left" or "left_outer". The `crossJoin()` method creates a Cartesian product, not a left join. The `merge()` method is not part of Spark's DataFrame API but is from pandas. The `leftJoin()` method does not exist in Spark's DataFrame API, and there is no standalone `join()` function in Spark; the `join()` method is called on DataFrame objects. Therefore, the correct answer is A.

Author: LeetQuiz Editorial Team