The correct answer is: A. primary key
A primary key is a column or group of columns in a table that uniquely identifies each row in the table. It is a column that cannot have duplicate values.
A keyword is a word or phrase that is used to identify a document or other piece of information. It is often used in search engines to help users find the information they are looking for.
A field name is the name of a column in a table. It is used to identify the column and to make it easier to reference the data in the column.
While a keyword or field name can be used to identify a record in a table, only a primary key can uniquely identify each record.