Question: what part of the ph probe is sensitive to hydrogen ion concentration
[{'answer': 'pH electrode', 'provenance': [{'wikipedia_id': '1499906', 'title': 'Glass electrode', 'start_paragraph_id': 1, 'start_character': 219, 'end_paragraph_id': 1, 'end_character': 231, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '1499906', 'title': 'Glass electrode', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 551, 'bleu_score': 0.978606533029418, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17458759729450497064}, 'section': 'Section::::Abstract.'}]}]