The task is to apply Dynamic Data Masking (DDM) to an existing column.

1. Box 1 (ALTER): The ALTER TABLE command is required because the dbo.CreditCard table already exists, and we are modifying its properties.
2. Box 2 (ALTER): The ALTER COLUMN clause is used within ALTER TABLE to specify which column's definition is being modified—in this case, to add a mask.
3. Box 3 (PARTIAL): The PARTIAL function is the specific DDM function that masks data by showing a defined number of leading (prefix) and trailing (suffix) characters. The syntax PARTIAL(2, "XXXXXXXX", 4) directly maps to the requirement to show the first two characters (prefix=2) and the last four characters (suffix=4).

The final correct T-SQL statement would be: ALTER TABLE dbo.CreditCard ALTER COLUMN [CreditCard] ADD MASKED WITH (FUNCTION = 'PARTIAL(2,"XXXXXXXX",4)')

Microsoft Learn (Microsoft Fabric Documentation). Dynamic data masking in Microsoft Fabric data warehousing.

Section: "Implement dynamic data masking"

Explanation: This official documentation confirms that Dynamic Data Masking is the correct feature to use in a Fabric data warehouse to limit sensitive data exposure to non-privileged users (like the data analysts with the Viewer role).

Microsoft Learn (T-SQL Documentation). Dynamic Data Masking.

Sections: "Masking Functions" (sub-section "Partial") and "Examples" (sub-section "Adding a mask to an existing column").

Explanation: This document defines the T-SQL syntax. It shows that ALTER TABLE ... ALTER COLUMN ... ADD MASKED is the correct syntax for adding a mask to an existing column. It also explicitly defines the partial(prefix, [padding], suffix) function as the method for exposing a set number of first and last characters, which matches the question's requirement.