c, but this is rather circular and dependent on what you think a civilisation is. All of the above, in greater or lesser degrees, would be the best answer. I suppose that dense urban lifestyles can only exist supported by civilisation, but civilisations can exist without a dense urban lifestyle.
Our funeral services would look like superstitious burial rituals to an objective outsider
Rural or agricultural lifestyles are necessary to support urban agglomeations.
Many, but not all, civilisations have a common language.