Why is it particularly difficult to separate oil and water once
they are mixed?

First of all, the water and oil do not mix because they are very different chemically. The water is polar, which means each molecule has parts with small positive and negative electric charges. Oil is very nonpolar, which is why it doesn't mix well with polar liquids.

Explanation:

correct answers:

c. they use panels.

d. they include images and words.

e. they contain gutters.