The correct answer is C. compute.ops_on_diff_frames. This configuration option in Pandas API on Spark controls whether operations between different DataFrames are allowed. It's disabled by default to prevent potentially expensive operations that could degrade performance, especially with large datasets. Enabling it permits such operations when necessary for your analysis.

How to Enable Operations:

1. Import: from pyspark.pandas import config
2. Set Option: config.set_option('compute.ops_on_diff_frames', True)

Caution: Use this option carefully, as enabling operations between different DataFrames can lead to performance issues. Consider alternatives like joining DataFrames or using explicit Spark transformations for better performance.