Question: when did namibia choose english as its main national language
[{'answer': '1990', 'provenance': [{'wikipedia_id': '20173128', 'title': 'Languages of Namibia', 'start_paragraph_id': 1, 'start_character': 320, 'end_paragraph_id': 1, 'end_character': 324, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '20173128', 'title': 'Languages of Namibia', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 642, 'bleu_score': 0.943950247594541, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4010576938385648598}, 'section': 'Section::::Abstract.'}]}]