Question: the first series of extrasolar planets that were discovered were found by which method
[{'answer': 'radial velocity variations', 'provenance': [{'wikipedia_id': '28582968', 'title': 'Discoveries of exoplanets', 'start_paragraph_id': 3, 'start_character': 33, 'end_paragraph_id': 3, 'end_character': 59, 'bleu_score': 1.0, 'section': 'Section::::1988–1994.\n'}]}, {'provenance': [{'wikipedia_id': '28582968', 'title': 'Discoveries of exoplanets', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 472, 'bleu_score': 0.928680631194693, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9746242926515037941}, 'section': 'Section::::1988–1994.\n'}]}]