Order terminating parental rights is reversed where the court's denial of the parents' opportunity to cross-examine the social service agency-s witnesses who testified the minor children were adoptable was prejudicial error since a parent who is a party to a hearing conducted under Welfare and Institutions Code section 366.261 has a due process right to conduct examination and test the sufficiency of evidence offered by a social service agency on the issue of adoptability, an issue on which the agency bears the burden of proof.