I'm not completely sure but I think the answer would be c
Some you wouldn't see by stepping outside, but it gives you a general understanding of what you should be looking for.
Hope this helps!
Computer modeling is used in biological studies because it can be used to make models that can be used to hold data.
Like objects attract each other
<em>carbon has four valence electrons in its outermost shell .. which makes it able to form four bonds to complete its valence shell ..
it forms large number of chains with its own self which makes it useful .. also it forms bonds with oxygen and hydrogen forming large organic compounds of great importance ..</em>