Explanation
This is because Bulk API is a RESTful API that is optimized for loading or deleting large sets of data asynchronously. By processing jobs in parallel mode, you can take advantage of the multiple resources available on the Salesforce platform and speed up the data load. The other options are not suitable for this scenario because:
B, Contact Salesforce support to schedule performance load, is not a valid option as Salesforce does not offer such a service. You are responsible for optimizing your own data load performance.
C, Use Bulk API to process jobs in serial mode, is a slower option than parallel mode as it processes one batch at a time. This is only recommended when you have dependencies between records or when you want to preserve the order of records.
D, Use Bulk API to process jobs in high performance mode, is not a valid option as there is no such mode in Bulk API. You can only choose between parallel and serial modes.
References:
Introduction to Bulk API 2.0 and Bulk API
Use Bulk API 2.0 Unit