Answers

2015-12-13T22:38:21+05:30
Mostly drinks are acidic in nature
so
if they have direct contact with teeths , may be harmful
in order to avoid this
straws are used
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2015-12-14T08:52:12+05:30
Constant, prolonged exposure to sweets and drinks may cause cavities and tooth decay. straws avoid this tooth decay as less time will spend in contact with teeth.  that is y it is used to drink soft drinks. 
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