Answer: ```python (storesDF.withColumn("openTimestamp", col("openDate"). cast("Timestamp")) . withColumn("dayOfYear", dayofyear(col("openTimestamp)))) ```

Option D is correct because the openDate column is stored in UNIX epoch seconds, which are not directly usable with Spark’s date functions. To get the day of the year, the value must first be converted to a Timestamp type. In Option D, openDate is cast to "Timestamp" to create a new column openTimestamp, and then dayofyear is applied to this timestamp column to correctly return the integer day of the year. Other options are incorrect because they either apply dayofyear directly to the integer epoch values without converting (B, C), use Date instead of Timestamp which can cause incorrect parsing or errors (A), or perform string slicing that does not calculate real dates (E). Rule to remember: When working with UNIX epoch times in Spark, always cast them to Timestamp before using any date or time functions.

Author: LeetQuiz Editorial Team