Explanation:
A database cursor is a special control structure that facilitates row by row processing of records in a result set. It allows the application to retrieve and manipulate data from a database one row at a time. The cursor acts as a pointer to the current row in the result set, and it can be moved forward or backward to access different rows.

Key Points:
- Row by row processing: A database cursor allows the application to process each row in a result set one at a time. This is useful when dealing with large result sets or when the application needs to perform specific operations on each row individually.
- Result set: A result set is the set of rows returned by a database query. It represents the data that matches the specified conditions in the query. The cursor is used to navigate through this result set.
- Pointer to the current row: The cursor keeps track of the current row in the result set. It allows the application to access the data in the current row and perform operations on it. The cursor can be moved forward or backward to access different rows in the result set.
- Retrieving and manipulating data: The cursor provides methods for retrieving data from the current row, such as getting the value of a specific column. It also allows the application to update or delete the current row, and insert new rows into the result set.
- Connection: A database connection is a communication pathway between the application and the database server. It is used to establish a connection, execute queries, and retrieve data from the database. While a connection is necessary to interact with the database, it is not specifically designed for row by row processing like a cursor.
- Tuple: A tuple is a collection of fields or attributes that represents a single record in a database table. It is not a control structure for row by row processing like a cursor.

Therefore, the correct answer is option 'B', a database cursor. It is specifically designed to facilitate row by row processing of records in a result set.