Before cities were established, most people had to learn how to be self-sufficient,supplying all the necessities of life by themselves.

Some people found it was easier to concentrate on producing one or just a few goods, and trade the surplus to other villagers for the other items they needed to live. People were willing to travel farther and farther to exchange goods with other people, and  in this way, "trade" was the catalyst for exploration adn cross-cultural interaction. "Trade" was also the cause for many cities to grow in wealth and power, as merchants from all over flocked to their marketplaces. This also raised the demand for improved ways to carry goods over long distances.

Q:which of the following is correct according to the passage?

(a) Traders were unwilling to journey very far from their base.

(b) Peolpe should produce all the things they needed to survive.

(c)Expeditions were initiated in order to learn about culture.

(d) Transportation advanced to accomodate commerce.