To answer this question, the user needs to understand the basics of SQL tuning and database optimization.

The correct answer is:

B. They may be able to be tuned to use an index

Explanation:

A full-table scan is a process in which the database engine reads all the rows of a table to find the relevant data. This can be a time-consuming process, especially for large tables. Full-table scans are not always sub-optimal, but they can be inefficient if the table is not properly indexed. When a table is not indexed correctly, the database engine must read every row of the table to find the relevant data, even if only a small subset of the data is needed.

Therefore, searching for full-table scans is critical to SQL tuning because it allows a database administrator to identify tables that are not properly indexed. Once identified, the administrator can then tune the full-table scan to use an index, which can improve performance and reduce the time it takes to retrieve the data.

Option A is incorrect because a full-table scan does not indicate an optimized execution plan. It may be the only option available, but it is not necessarily optimized.

Option C is incorrect because a full-table scan is not something that should be normalized from the database design. It is a method of retrieving data from a table and can be optimized through proper indexing.

Option D is incorrect because a full-table scan is not always sub-optimal. It depends on the size of the table and how well it is indexed.