For a long time Chester Carlson carried around his little bl

For a long time Chester Carlson carried around his little black box----the invention over which he had worked and struggled for years.He showed it to the directors of twenty-one large American corporations,such as “General Electric,International Business Machines(IBM),Lockheed,and RCA.”
Nobody wanted it.
Nobody wanted to invest a penny in it.
It must be painful for those directors to think of Chester Carlson now.For the little black box is the heart of the multi-billion-dollar Xerox Corporation.Carlson is the inventor of “xerography” (from two Greek words meaning “dry writing”),the dry-printing process used in thousands and thousands of offices,businesses,industries,universities,shops,and government agencies around the world.
Thanks to Carlson,it now takes minutes to copy a document which,twenty years ago,would have kept a secretary busy for a whole day.And for a few pennies anyone can have a copy of anything from cooking recipes to Greek poetry.More than thirty billion such copies are made each year.
When Chester Carlson went to work in a patent office in 1930,the copying methods were slow,dirty,and expensive.In his job,Carlson had to make many copies of patents for inventions.One night,after working late and painfully,he decided that somebody had better find an easier way to do it.He went to work in the kitchen of his apartment with measuring cups and cooking pots.By 1937,having developed a simple form of xerography,he applied for his first patent on the process.
1）Chester carlson was_
A )a director of an American corporation
B)an inventor of a copying maching
C)a company salesman
D)an office clerk in a company
2)at first nobody wanted this little black box because_
a)it was considered to be of no value
b)very little was known about it
c)people thought it was not a worth-while investment
d)all of the above
3)how long did it take Carlson to complete his research into this dry-printing process?
a)a lifetime
b)seven years
c)twenty years
d)not mentioned in the passage

d