Question: who is the head of the department of homeland security 2017
[{'answer': 'Kirstjen Nielsen', 'provenance': [{'wikipedia_id': '212926', 'title': 'United States Secretary of Homeland Security', 'start_paragraph_id': 2, 'start_character': 86, 'end_paragraph_id': 2, 'end_character': 102, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '55166207', 'title': 'Kirstjen Nielsen', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['Nielsen was confirmed as secretary of homeland security on December 5, 2017', 'Nielsen was confirmed as secretary of homeland security on December 5, 2017.', 'Kirstjen Michele Nielsen (born May 14, 1972) is an American attorney who is a former United States']}}]}]