●A basic premise of OGSA is that everything is (66) by a service：a network enabledentity that (67) some capability through the exchange of messages.Computational resources，storage resources，networks，programs，databases，and so forth are all (68) .This adoption of auniform. service-oriented model means that all components of the environment are virtual.Morespecifically，OGSA represents everything as a Grid service：a Web service that conforms (69) a set of conventions and supports standard interfaces for such purposes as lifetime management.This core set of consistent interfaces，from which all Grid services are implemente D.(70) theconstruction of hierarchical，higher-order services that can be treated in a uniform. way across layersof abstraction. (66) A.defined B.represented C.used D.passed (67) A.provides B.have C.expands D.limits (68) A.elements B.objects C.services D.capability (69) A.of B.to C.as D.from (70) A.forms B.groups C.consist D.Facilitates