http://hl7.org/fhir/StructureDefinition/questionnaire-referenceResource|5.2.0

Where the type for a question is \"Reference\", indicates a type of resource that is permitted.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/code
Extension.value[x].binding.valueSethttp://hl7.org/fhir/ValueSet/resource-types