![](https://cos-cdn.shuashuati.com/pipixue-wap/2020-1230-1107-56/ti_inject-812ce.png)
By saying '...those raw materials exist already in abundance in every nation', the author is referring to ______.
A.
hosts and staff to welcome visitors
B.
people, the environment and culture
C.
the capital used to build the tourism industry
D.
the environmental resources to build up tourism