Which of the following is one of the only two DOCa wine regions in Spain?

Rioja is recognized as one of the only two Denominación de Origen Calificada (DOCa) wine regions in Spain, which is a classification that denotes a high level of quality and regulatory oversight in winemaking. The status of DOCa is granted only to regions that have consistently produced wines of superior quality over many years and have stringent regulations governing the production process. Rioja has a long history of winemaking and has developed a reputation for excellence, particularly for its red wines made primarily from the Tempranillo grape.

The significance of this classification lies in its role in ensuring that consumers can trust the quality and origin of the wines produced within such regions. The other wine regions listed do not carry the DOCa designation; Ribera del Duero is classified as a Denominación de Origen (DO), Valdepeñas is also a DO, and Rueda is a DO known primarily for its white wines, particularly those made from Verdejo. These classifications indicate quality but do not meet the stringent criteria required for DOCa status.