important attribute of assurance service

Which of the following statements relating to attest and assurance services is not correct?
a. Independence is an important attribute of assurance service providers.
b. Assurance services can be performed to improve the quality or context of information for decision makers.
c. Financial statement auditing is a form of attest service but it is not an assurance service.
d. In performing an attest service, the CPA determines the correspondence of the subject matter (or an assertion about the subject matter) against criteria that are suitable and available to users.