Glass is everywhere in our lives. It is so common 【21】______ we hardly think about it. We 【22】______ it when we look out of th

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问题      Glass is everywhere in our lives. It is so common 【21】______  we hardly think about it. We 【22】______  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 【23】______  . Glass 【24】______  in homes, schools, businesses, industry, and automobiles.
     Fortunately for us, glass is 【25】______  very inexpensive materials. The main material is sand from quartz rock. The mixture is heated until it becomes a syrupy 【26】______  . When the liquid cools, it becomes glass.
     No one knows 【27】______  first discovered glass or how. Early humans used obsidian, a natural glass 【28】______  by volcanoes, to make tools and jewelry. People probably began making glass themselves around 3000 B.C. in Syria. Then in a war 【29】______  Egypt and Syria in 1400 B. C., Syria became part of Egypt. The Egyptians took Syrian glassmakers 【30】______  to Egypt, and over the centuries the entire eastern Mediterranean area became a glassmaking center.
     Probably around 300 B.C. the blowpipe 【31】______ . Egyptian glassmakers developed the use of the blowpipe. They specialized 【32】______  beautiful jewelry, dishes, and other containers.
   The Romans soon started making their own glass. Then they 【33】______  that glass could be used to make windows. 【34】______  centuries later, Europeans made magnificent church windows 【35】______  colored glass.
      【36】______  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 【37】______  flying in all directions. This invention is very useful 【38】______  automobile windows.
     Today most glass is made 【39】______  machines in large factories. No one 【40】______  it. People use television and computers to control the machines.
【36】

选项 A、Because
B、As
C、For
D、Since

答案D

解析 since 1900意为“从1900年以来”,符合上下文句意。
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