Question: what does it mean to jackknife a trailer
[{'answer': 'folding of an articulated vehicle', 'provenance': [{'wikipedia_id': '2160269', 'title': 'Jackknifing', 'start_paragraph_id': 1, 'start_character': 26, 'end_paragraph_id': 1, 'end_character': 59, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2160269', 'title': 'Jackknifing', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 692, 'bleu_score': 0.9253595725203031, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4891989119768341816}, 'section': 'Section::::Abstract.'}]}]