Question 23 is based on the passage you have just heard.

听力原文    

        Maybe you carry the most powerful passport in the world, or perhaps the rarest passport. Whatever the case, your passport will likely be one of four colors: red, blue, green or black, although there are slight variations. Switzerland’s passport is dark red, for example, (22) [while most European countries prefer a shade of red that’s almost brown.] There are no official rules regarding passport colors, (23) [but countries follow a certain set of norms when designing them.] The International Civil Aviation Organization, which works to define the principles of air travel, suggests that countries use a suitable type, size and style for official documents like passports. There are also a few compulsory aspects of passports. They must be made from a material that bends. They should be able to be read by a machine at temperatures ranging from 10℃ to 50℃ and conditions where the air can be extremely dry or moist. Despite these existing recommendations, there is nothing regarding the cover color. Why? (24) [Simply put, countries stick to darker and more conservative colors because they appear more official] and they can also hide dirt and wear. While there’s little innovation when it comes to passport cover color, the same cannot be said for the pages. (25) [The passports of many countries contain images of their well-known geographical features and wildlife, which also function as security features as some are only visible under a special light.]

23. What does the passage say about the design of passports?（关于护照的设计，文章说了什么？）

解析：D。录音中提到，各国在设计护照时遵循一定的规范，D项中的follow some common standards是对录音中follow a certain set of norms的同义转述，故D项正确。

错项排除：录音中提到，各国都坚持使用较深、较保守的颜色，因为这样不显脏、耐磨损，但并没有说耐磨损是护照的必要设计标准，故A项错误。录音中表示，国际民用航空组织建议各国对护照等官方文件使用合适的类型、大小和样式，但并没有说必须要大小相同，故B项错误。录音中提到，护照必须由能够弯曲的材料制成，但并没有说材料是否稀有，故C项错误。