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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getVariantAnnotationSets(self, datasetId):
 """ Returns the list of ReferenceSets for this server. """

        # TODO this should be displayed per-variant set, not per dataset.
        variantAnnotationSets = []
        dataset = app.backend.getDataRepository().getDataset(datasetId)
        for variantSet in dataset.getVariantSets():
            variantAnnotationSets.extend(
                variantSet.getVariantAnnotationSets())
        return variantAnnotationSets