What happens when you put water and oil

When you put oil and water together they'll separate. The oil will float at the top because it is less dense than water.
Oil and water don't mix together because water molecules are more attracted to each other than to oil molecules. 

So to keep this answer short when you put water and oil together it will separate and the oil will only be at the top. 

Hope this helps :)
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The correct answer is b

Decomposition is the cycle at which bacteria breaks down any organic material into the soil