问题
选择题
The companies are working together to create _________ they hope will be the best means of transport in the 21st century.
A．which
B．that
C．what
D．who
答案
C
what在此引导宾语从句，且在宾语从句中用作主语，其中的they hope可视为插入成分。句意为：这些公司齐心协力希望制造出21世纪最好的交通工具。