It may be necessary to stop（）(每隔一定时间) in the learning process and go back to the difficult points in the lessons.

填空题There’s a man at the reception desk who seems very angry and I think he means（）(想找麻烦).

填空题We’d like （）(预订一张餐桌) five for dinner this evening.

填空题The price of beer（）(从50美分到4美元不等) per liter during the summer season.

填空题Although punctual himself, the professor was quite used（）(习惯了学生迟到) his lecture.

填空题Over a third of the population was estimated（）(无法获得) to the health service.