When implementing a custom pricing plan step for attribute-based pricing in the Default Pricing plan in Salesforce Industries CPQ, the step should be placed: D. Between the step Initialize Pricing Context and the step Load Price List Entries: This sequence allows for the correct application of context-specific attributes before price list entries are loaded, ensuring that all attribute conditions and dependencies are established prior to fetching and applying pricing from the price list.

This placement is crucial for effectively leveraging attribute-based pricing mechanisms, as it aligns the pricing data load with the initialized pricing context, allowing for dynamic pricing adjustments based on predefined attributes.