All the above are evidence for the hypothesis
The statement which best explains why carbon is present in so many kinds of molecules is because <u>it can form four covalent bonds.
<em /></u>It isn't rare on Earth, so A is incorrect. It has valence electrons, so C is incorrect. It cannot become an ion, so D is incorrect.<u>
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A situation where friction would be desirable is rubbing your hands together to make them warm in the winter time.
I am not entirely sure what you mean by "responding variable" but I'm going to guess it was the vinegar since it has been used as a perservative for years.
Hope that helps in some way.
