For questions 6-30, read the text below and think of the word which best fits each space.
Use only one word in each space. There is an example at the beginning (0).
GLASS
Perhaps (0) __one__of the commonest man-made substances is glass. In fact, it is (16)
__________________ common that few people appreciate its unique qualities. Glass is (17)
__________________ hard and transparent. It does not expand when heated, it is a very poor
conductor and it is resistant to all acids (18) __________________ hydrofluoric acid, which
dissolves it.
(19) __________________ knows exactly where or when the manufacture of glass began. (20)
__________________ is known, though, is that there were skilled glass makers in ancient Egypt
who practised it as (21) __________________ as 2000 BC, if not earlier. The Romans are also
known to (22) __________________ been particularly good (23) __________________ making
glass.
Glass is (24) __________________ from sand, an alkali and other ingredients which can (25)
__________________ colour it or change its properties. These changes are usually achieved (26)
__________________ adding certain chemicals during the process or placing thin layers of other
substances (27) __________________ two sheets of glass. The nature of the glass produced also
depends (28) __________________ the quality of the ingredients used.
Nowadays, one of the main uses of glass is in windows, which to us would seem to (29)
__________________ quite logical. However, the art of making glass was known long (30)
__________________ it was considered suitable for windows.
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