Solution. Models are being used as a simplified representation of an object, idea, or an event that is too complex, too small, or too big to study. Scientists use models in order to show how a certain phenomenon occurs and to answer the questions regarding it.
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The answer is, b. other substances
Digging and chopping similar to the pickaxe.
An economy based on trade
I'd say "All types are popular , it just depends on personal preference" but the MOST popular form of the news today would have to be "Television News" try going with that