Question: what did the soviets build to separate east and west berlin
[{'answer': 'The Berlin Wall', 'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 15, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 823, 'bleu_score': 0.6804619207583441, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14506824188020035248}, 'section': 'Section::::Abstract.'}]}]