The correct answer is C. MEMORY_ONLY. This caching level ensures that the DataFrame is stored in memory only, facilitating quick access and processing. Accessing data from memory is significantly faster than from disk, which can greatly enhance performance. However, it's important to consider the size of your DataFrame; for very large DataFrames that exceed available memory, using MEMORY_AND_DISK might be more efficient to avoid memory overflow. DISK_ONLY stores the DataFrame on disk, which is slower, and OFF_HEAP involves storing data off the JVM heap, which is not relevant to storing data in memory only.