Which two sfdx commands can be used to add testing data to a Developer sandbox?

The `sfdx force:data:bulk:upsert` command allows developers to import a large volume of data into Salesforce objects using the Bulk API, which is efficient for populating a sandbox with significant test datasets.

There is no standard `sfdx force:data:object:upsert` command; the command for upserting a single record or small amounts of data is `sfdx force:data:record:upsert`.

The `sfdx force:data:tree:upsert` command is used to import data that has parent-child relationships, typically defined in a JSON file, which is crucial for creating realistic test data scenarios across multiple related objects.

There is no standard `sfdx force:data:async:upsert` command; asynchronous operations are often handled implicitly by `bulk` commands, but 'async:upsert' is not a specific SFDX command.