Option D: Use Test.getStandardPricebookId() to get the standard price book ID.
Correct Answer.
The Test.getStandardPricebookId() method returns the ID of the standard price book, which can be used in test classes without using SeeAllData=true.
This allows the test to access and use the standard price book in a controlled manner.
Using SeeAllData=true is discouraged as it can make tests dependent on org data.
Deleting data in tests can have unintended consequences.
Option B: Use Test.loadData() and a static resource to load a standard price book.
Unnecessary.
There's no need to load a standard price book via Test.loadData() when Test.getStandardPricebookId() is available.
Option C: Use @TestVisible to allow the test method to see the standard price book.
Incorrect Use of @TestVisible.
@TestVisible is used to expose private members to test classes, not to access data.
Conclusion:
The developer should use Test.getStandardPricebookId() to get the standard price book ID, which is Option D.
Reference:
Accessing the Standard Price Book in Tests
Option A: Use @IsTest(SeeAllData=true) and delete the existing standard price book.
Not Best Practice and Risky.