A simple primary key is, by definition, a key composed of a single attribute (field or column). This is the most direct and accurate term for a primary key that consists of only one field. It stands in contrast to a composite or compound key, which is formed by combining two or more attributes to uniquely identify a record. The term "simple" specifically describes the structural composition of the key itself.

B. Partition: This term refers to database storage strategies for dividing large tables into smaller parts, not the number of fields in a primary key.

C. Stable: A stable key is one whose value does not change over time. This describes a behavioral characteristic, not its structure (single vs. multiple fields).

D. Meaningless: A meaningless (or surrogate) key is an artificial key with no business significance. This describes its semantic nature, not its composition.

1. Elmasri, R., & Navathe, S. B. (2017). Fundamentals of Database Systems (7th ed.). Pearson. In Chapter 3, Section 3.2.2, "Constraints on Relational Databases," the text distinguishes between keys formed from a single attribute (simple keys) and those formed from multiple attributes (composite keys).

2. Coronel, C., & Morris, S. (2019). Database Systems: Design, Implementation, and Management (13th ed.). Cengage Learning. Chapter 3, "The Relational Database Model," Section 3.4.1, "Keys," defines a simple key as "a key that is composed of a single attribute."

3. Ullman, J. D., & Widom, J. (2008). A First Course in Database Systems (3rd ed.). Pearson Prentice Hall. Chapter 2, "The Relational Model," Section 2.3.1, "Keys," explains that a key can consist of one or more attributes, implicitly defining a single-attribute key as the simplest form.