Question: what are the chief commercial tree crops of liberia
[{'answer': 'natural rubber', 'provenance': [{'wikipedia_id': '47202200', 'title': 'Agriculture in Liberia', 'start_paragraph_id': 2, 'start_character': 20, 'end_paragraph_id': 2, 'end_character': 34, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'bananas', 'provenance': [{'wikipedia_id': '47202200', 'title': 'Agriculture in Liberia', 'start_paragraph_id': 2, 'start_character': 51, 'end_paragraph_id': 2, 'end_character': 58, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'palm oil', 'provenance': [{'wikipedia_id': '47202200', 'title': 'Agriculture in Liberia', 'start_paragraph_id': 2, 'start_character': 63, 'end_paragraph_id': 2, 'end_character': 71, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Timber', 'provenance': [{'wikipedia_id': '47202200', 'title': 'Agriculture in Liberia', 'start_paragraph_id': 2, 'start_character': 73, 'end_paragraph_id': 2, 'end_character': 79, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '47202200', 'title': 'Agriculture in Liberia', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 534, 'bleu_score': 0.976327165973018, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7554636598737917033}, 'section': 'Section::::Abstract.'}]}]