Assertion. There can be multiple options for choosing a primary key in a data table.

Reason. All attribute combinations inside a data table that contain unique values for each row, are the candidate keys.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
There can be more than one attribute in a relation possessing the unique identification property. All attribute combinations inside a relation that can serve as a primary key are candidate keys, as they are candidates for the primary key position.