下列短文中有十个空白，每个空白有四个选项。根据上下文要求选出最佳答案。

Henry’s job was to examine cars which crossed the frontier to make sure that they were not smuggling anything into the country. Every morning，except at weekends，he (11) see a factory worker coming up the hill towards the frontier， (12) a bicycle with a big load of old straw on it. When the bicycle arrived the frontier，Henry used to stop the man and order him to take the straw off. Then he would examine the straw very carefully to see (13) he could find anything，after which he would look in all the man’s pockets before he let him tie the straw up again. The man would then put it on his bicycle and go off down the hill with it. Although Henry was always (14) to find gold or jewelry or other valuable things hidden in the straw，he never found (15) ，even though he examined it very carefully. He was sure that the man was smuggling something，but he was not (16) to imagine what it could be. Then one evening，after he had looked through the straw and emptied the factory worker’s pockets (17) usual，he said to him，“Listen，I know that you are smuggling things (18) this frontier. Won’t you tell me what it is that you’re bringing into the country so successfullyI’m an old man，and today’s my last day on the job. Tomorrow I’m going to (19) . I promise that I shall not tell anyone if you tell me what you’ve been smuggling. ”The factory worker did not say anything for (20) . Then he smiled，turned to Henry and said quietly：“Bicycles. ”