The correct answer is - d. Each answer shown is correct.
The formation of a civilization is a process in which multiple things are included. The basis for it is the agriculture, as it enabled the people to start settling in one place. But in order for it to be classified as a civilization, certain other things have to appear, things that would enable progress, development, higher level of thinking, architecture. The basis for these things to occur are the building of the planned cities, that already showed a level of advancement, as well as the written language, which is the trait that contributed the most to the development of the people, thus becoming a civilization.
