What is sucking sbc-xjzf-pvcb

only for g I r l s

interested in showing
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draw into mouth by contrasting the muscles of the lips and mouth to make a partial vaccum

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.