EXERcISE 15
glass is everywhere in our lives.It is somon __1_ we hardly think about it.we _2__ it when we look out of the window and if we wear glasses.we drink from it and sometimes eat from it.The light in our homeses through glass windows in the daytime and from glass lights _3__.glass __4_ in homes,schools,businesss,industry,and automobiles.
Fortunately for us,glass is __5_ very inexpensive materials.The main material is sand from quatz rock.The mixture is heated until it bes a syrupy _6__. when the liquid cools,it bes glass.
No one knows __7_ first discovered glass or how.Early humans used obsidian,a natural glass __8_ by volcanoes,to make tools and jewelry.People probably began making glass themselves around 3000 B.c. in Syria.Then in a war __9_ Egypt and Syria in 1400 B.c,Syria became part of Egypt.The Egyptians took Syrian glassmakers __10_ to Egypt,and over the centuries the entire eastern mediterranean area became a glassmaking center.
Probably around 300 B.c. the blowpipe __11_. Egyptian glassmakers developed the use of the blowpipe.They specialized _12__ beautiful jewelry,dishes,and other containers.
The Romans soon started making their own glass.Then they _13__ that glass could be used to make windows.__14_ centuries later,Europeans made magnificent church windows __15_ colored glass.
__16_ 1900panies have developed many new types of glass.Safety glass is a sandwich of glass and plastic.If it breaks,the pieces stay together _17__ flying in all directions.This invention is very useful _18__ automobile windows.
Today most glass is made __19_ machines in large factories.No one _20__ it. People use television andputers to control the machines.
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