Question 20 is based on the passage you have just heard.

      Wherever you go and for whatever reason, it's important to be safe. (19) While the majority of people you will meet when travelling are sure to be friendly and welcoming, there are dangers—theft being the most common.

    Just as in your home country, do not expect everyone you meet to be friendly and helpful. It's important to prepare for your trip in advance and to take precautions while you are travelling. (20) As you prepare for your trip, make sure you have the right paperwork. You don't want to get to your destination only to find you have the wrong visa, or worse, that your passport isn't valid any more. Also, make sure you travel with proper medical insurance, so that if you are sick or injured during your travels, you will be able to get treatment. If you want to drive while you are abroad, make sure you have an international driver's license.

    (21) When you get to your destination, use official transport. Always go to bus and taxi stands. Don't accept rides from strangers who offer you a lift. If there is no meter in the taxi, agree on a price before you get in. If you prefer to stay in cheap hotels while travelling, make sure you can lock the door of your room from the inside. Finally, remember to smile. It's the friendliest and most sincere form of communication, and is sure to be understood in any part of the world!

(20). What is the most important thing to do when you prepare for your trip abroad?

解析：细节理解题，问题为：准备出国旅行时最重要的事是什么？根据文中As you prepare for your trip, make sure you have the right paperwork.可知，准备旅行时，准备好文书文档。其中的关键词是make sure和the right paperwork，由此可知正确选项是D（拥有正确的文档），其中paperwork和documents是同义替换，都表示“文档”。