Question

Read the passage and answer the question. Passage: A personal assistant's day is measured in minutes, not hours. The doctor she works for may see forty patients before lunch, dictate a dozen letters between consultations, and chair a committee in the evening, and every one of those tasks passes through her desk. Good time management for such an assistant is therefore not about working faster; it is about deciding what matters first. The most useful habit is the morning list: ten minutes spent ordering the day's work by urgency and importance saves an hour of confusion later. The second habit is the buffer, keeping fifteen minutes free between appointments so that one delayed patient does not push the whole day off course. The third is learning to say no, politely but firmly, to work that belongs to someone else's desk. Assistants who master these habits report the same result: the day feels shorter, the work gets done, and the doctor's trust grows. Time, after all, is the one resource a hospital cannot buy more of. The word 'buffer' in the passage is closest in meaning to: