The correct answer is A. WSDL.
WSDL (Web Services Description Language) is an XML-based language that describes a web service. It defines the service interface, how to bind information, and the nature of the component’s service or endpoint.
B. SCD is a Service Component Definition Language. It is a language used to describe the components of a service-oriented architecture (SOA).
C. XML is a markup language that is used to create documents. It is not specifically used to describe web services.
D. None of the mentioned is not a correct answer.