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needn’t can’t aren’t don’t
Glass is very useful because it has many unusual qualities. Light signals have changed the use of glass in industry. Glass fibers have reduced the cost of telephone communication. The use of glass fibers to carry telephone messages is an interesting new development.
to clean, needn’t cleaning, don’t clean, aren’t cleaned, can’t
glass fiber is less expensive glass fiber delivers messages directly glass fiber is more up to date glass fiber is easier to make
glass fiber is less expensive glass fiber delivers messages directly glass fiber is more up to date glass fiber is easier to make
electrical signals must first be changed' into light signals and then into sound the light signals have to be changed directly into sound light must first be changed into electrical signals and then into sound neither the light nor the electrical signals have to be changed in any way
made into make into making made of
has been put into actual use was first put into actual use in 1977 had been repeatedly experimented on before 1977 was put on experiment in 1977
Can; must Must; need May; must Need; can
Could; may Can; must May; must Can; can
sound signals light signals electrical signals any signals
made taken recorded recycled
Can’t; can’t Could; won’t May; daren’t Shall; may
glass of milks glasses of milk glass of milk glasses of milks
Could; may Can; can May; must Can; must
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