Olive oil is more dense than c so it will sink to the bottom of the container.
Ethanol and olive oil are immiscible and olive oil is denser than etahnol. Add water to the mixture. Water is miscible with ethanol and is denser than both ethanol and olive oil.
As the water mixes with the etahnol, the density of the water/etahnol layer increases and eventually exceeds the density of the olive oil. This causes the layers in the container to invert and the olive oil to float.
Certain liquids are heavier, "dense", than others. When you attempt to mix two liquids which have different densities, they separate when you stop mixing them. The "heavier" liquid deposits itself on the bottom and the "lighter" liquid deposits itself on top. There exists a wide range of liquids with various densities. Molasses is most dense while alcohol is the least dense liquid.
To find out why do certain liquids mix together while other don't, consider these simple experiments from Educatall.com.