Rubber trees are tapped-that is, cuts are made in the bark so that the latex, a milk -like Juice, containing about 30 -40% rubber, can be obtained. The latex is then processed by exposing it to heat and wood smoke, or by mechanical means, so as to separate the rubber from the 'water, mineral salts, sugars, resins and protein matters. The rubber obtained in this way is known as, 'crude'-latex is extensively used in industry for making foam rubber, products. footwear, dolls etc. Untreated crude rubber is naturally soft and lacks the required strength for making into manufactured articles. To improve its strength and usefulness, it is vulcanised, or heated with sulphur, and the proportion of sulphur used determines the hardness and elasticity of, the rubber.
28 -From its description, we can say that latex ---- .
A) is a hard substance similar to rubber
B) must be a fairly thin, white liquid
C) is almost entirely pure rubber
D) is a by -product of rubber
E) is less useful than crude rubber
29 –It’s stated in the passage that untreated crude rubber is not used in industry, because --- .
A) its content of sulphur carries a nasty odour
B) its milky colour is undesirable
C) it lacks any kind of elasticity
D) it's neither hard nor strong enough
E) it contains far too many impurities
30 -In the process of vulcanisation, the principle is, that ---- .
A) the heat applied to the mixture should be high enough for rapid evaporation
B) the sulphur contained in the rubber should be extracted as much as possible
C) how hard or flexible the rubber becomes depends, on its sulphur content
D) the more sulphur is used, the harder and the more elastic the rubber becomes
E) the rubber can be separated from water by being heated at high temperatures
The origins of a written literature can be found in most of the civilisations of the ancient world; in India. China and among the Jewish people, whose great work of literature is the Old Testament of the Bible. However, it is the Greeks whose literature is taken to represent the start of Western literature. Their greatest single contribution was drama, a form of literature that has continued undiminished to the present day. Other literary forms that developed from the time of the ancient Greeks and Romans onward have been poetry in its many different styles and forms, the essay, biography and autobiography, and the novel. Other types of written work from these periods, dealing with such matters as history, philosophy, politics, religion, science and criticism may also be classified as literature from the point of view of style.
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