单选题 Glass is everywhere in our lives. It is so common 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 homes comes through glass windows in the daytime and from glass lights 3 . Glass 4 in homes, schools, businesses, industry, and automobiles.
Fortunately for us, glass is 5 very inexpensive materials. The main material is sand from quartz rock. The mixture is heated until it becomes a syrupy 6 . When the liquid cools, it becomes 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 1900 companies 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 and computers to control the machines.