Question: what is the purpose of t3 and t4
[{'answer': 'regulation of metabolism', 'provenance': [{'wikipedia_id': '18455584', 'title': 'Thyroid hormones', 'start_paragraph_id': 1, 'start_character': 193, 'end_paragraph_id': 1, 'end_character': 217, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '18455584', 'title': 'Thyroid hormones', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 940, 'bleu_score': 0.589982524886695, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10665566889804897771}, 'section': 'Section::::Abstract.'}]}]