问题补充：
The companies are working together to create they hope will be the best means of transport in the 21st century.
A. what
B. that
C. which
D. who
答案：
(答案→)A. what
B. that
C. which
D. who
解析：考查从句，从句they hope缺少宾语，所以从关系代词里选择引导词，ABCD都可以做宾语，但是表示的意思不同，what表示什么；that只起连接作用；which表示哪一个；who表示人，所以选A
