导致“公车上书”的直接原因是（    ）

用方框中所给单词的适当形式填空。

         As we know, there are many beautiful places in China, such as Hong Kong, Harbin. They attract a lot of people at home and abroad. But it's hard for ____ to choose where they can go. You can tell them ____ Guide to China, which ____ China in detail. If they have no chance to go through the book, you may show them advertisements for traveling, then after ____, they can decide where to go. They will have a good trip and take photos in ____ of it.

读“汽车产业链结构图”，结合所学知识，完成下列问题。