Although buses are______to depart at a certain hour, they are often late.
【正确答案】 A
【答案解析】schedule：(n．)时刻表，(v．)安排，计划，be scheduled to意为“预定，安排，计划做”；obligate：使有义务，强迫；request：要求；load：装载。根据句意可知，选A。