Today I'll be talking about the invention of the camera and photography.The camera is often thought to be a modern invention，but as early as 1727，a German physicist discovered that light darkens silver salt.Used as a camera，a big box was set up，and a small hole was cut in one side to let the light in；he made temporary pictures on the salt.Silver salt is still the base of the photographic film today.Then a French scientist made the first permanent picture by using a special piece of metal which was covered with silver salt.A photograph he made in 1862 still exists.
The painter De Gear improved the process by covering the metal also with placing the common salt which we can eat.That was in 1839，the official date of beginning of photographs.But the problem was the printing of the photographs.And it wasn't until other scientists developed the kind of photographic paper we now use that good prints were possible and photography became truly modern.In the 1870's，Matthew Bradey was able to take his famous pictures in American Civil War.In the 20's of this century，Georges Mann of the United States simplified film developing，and Dr.Edward Lane invented the socalled “Instant Camera”，which uses selfdeveloping film.If we say photography came into existence in 1839，it follows that it took more than 100 years for the camera to reach its present condition of technical refinement(密度)．
1．What discovery was the basis of photography?
A．Light darkens silver salt.
B．Light darkens natural salt.
C．Light darkens silver.
D．Light darkens selfdeveloping film.
2．How was the first permanent picture made?
A．By making use of special paper.
B．By adding common salt to silver salt.
C．By giving a slight colour to the silver salt.
D．By using a special piece of metal.
3．Which does the author regard as the official date of the beginning of photography?
A．1727. B．1826.
C．1839. D．1870.
4．According to the author，why is Matthew Bradey remembered today?
A．He was a soldier.
B．He took war photographs.
C．He painted portraits.
D．He designed a portable camera.
5．What did Doctor Edward Lane invent?
A．A cheap process of developing film at home.
B．A new kind of film.
C．An automatic printer.
D．An instant camera that develops its own film.