Question: what is composed of two layers of phospholipids associated with proteins
[{'answer': 'a thin polar membrane', 'provenance': [{'wikipedia_id': '158011', 'title': 'Lipid bilayer', 'start_paragraph_id': 1, 'start_character': 47, 'end_paragraph_id': 1, 'end_character': 68, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '158011', 'title': 'Lipid bilayer', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 913, 'bleu_score': 0.9687635332632951, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 40899088896242240}, 'section': 'Section::::Abstract.'}]}]