For many years, people have tended to think of natural resources as stacks of raw material piled up in a storehouse.A person with this sort of picture in his mind logically assumes that the more you use of any natural resources, the sooner you get to the bottom of the pile.Now we are beginning to discover that the idea of a storehouse does not correspond with reality.Instead, the fact seems to be that the first storehouse in which man found himself was only one in a series.As he used up what was piled in that first room, he found he could open a door into a much larger room.And as he used the contents of this larger room, he discovered there was another room beyond larger still.This concept of limitless raw material is not new.It is held by a number of persons.But it is an idea certainly not familiar to people at large.

　　It does not mean that progress is simple and that Utopia is near at hand.On the contrary, raw materials, no matter how vast in amount, do not become available resources until human thought and effort are applied to them.In a very real sense raw material; do 17ot exist, they are created, We know, for example, that in a region of great mineral wealth, people can live out their lives in extreme poverty if they do not realize the wealth exists or if they do not know how to get at it.It is use that makes it valuable.Even when the wealth is made available through technical means, the accelerating growth of populations and the enormous wastage of war are additional complications to consider.
We learn from the last sentence of the passage that _____.

A.the availability of raw materials also depends on war

B.continued expansion of scientific knowledge will prolong the usage of raw materials

C.political and social will also decide the availability of raw materials

D.war and population are severe problems